|A boycott of the polls by several opposition parties has thrown the process into disarray [Reuters]
Sudan is holding its first multi-party elections in 24 years.
Although 12 presidential candidates - representing 10 political parties and two independents - set out to contest the election, the subsequent boycotting of the polls by several opposition parties has thrown it into disarray.
Here we look at some of the key players in Sudanese politics.
|Omar Hassan al-Bashir - National Congress Party
Omar Hassan al-Bashir, 74, has been Sudan's president since he took power in a 1989 coup d'etat while he was an army officer. He then steered Sudan into an Islamist direction and continued a civil war with the south.
|Bashir has been president of Sudan since he took power in a 1989 coup [EPA]
In 2005 he brought Sudan closer to the international fold with a peace deal that ended more than two decades of north-south civil war. This landmark peace agreement with the south resulted in him sharing power with the Sudan People's Liberation Movement (SPLM).
However, that progress was overshadowed by the conflict in Darfur in which Bashir was accused of supporting the pro-government militias that allegedly committed atrocities against civilians.
The International Criminal Court has issued an arrest warrant for him for alleged war crimes and crimes against humanity in Darfur, charges which Bashir vehemently denies.
Bashir's defiance of the warrant, and implicitly of the West, has enhanced his appeal among parts of the northern electorate.
That, combined with the domination of the army, the security services and state media by his National Congress Party (NCP) has cemented his popularity across the country.
Colleagues describe Bashir as a back-seat leader who rallies crowds with populist rhetoric, often followed by a jig.
The boycott of the election by opposition parties has virtually ensured that he is the likeliest winner in the presidential race.
Bashir has promised to resolve the Darfur conflict through negotiations and to enhance relations with the south, even if it chooses secession in a 2011 referendum.
"If the people of South Sudan choose separation and not unity, I will be the first person to recognise that separation," he has said.
|Hassan al-Turabi - Popular Congress Party
Hassan al-Turabi, born in 1932, is a religious and political leader in Sudan. He is known for his progressive Islamist ideas, such as the embrace of democracy, bridging the Sunni-Shia gap, integrating art and music into Islam and expanding the rights of women.
|Turabi is an important religious figure and one time leader of the Muslim brotherhood [AP]
The Popular Congress Party (PCP), led by Turabi, split off in 2001 from the ruling NCP.
Turabi, who holds a PhD in law from the Sorbonne in Paris, joined Sudan's Muslim Brothers Organisation in the 1960s, which was founded in 1952 by students of the University of Khartoum as an extension of the Muslim Brotherhood Organisation of Egypt led by Hassan Al Banna.
Turabi led the brotherhood's party, the Islamic Charter Front (ICF), to a prominent role during the overthrow of the Abboud military regime in 1964.
In the elections of 1965 and 1968 it won a number of seats, but after the 1969 "socialist" revolution of Jafar Nimeri the ICF was banned and persecuted.
Following Nimeri's policy of "national reconciliation" in 1977 the activists of the dissolved ICF re-entered the political stage with Turabi taking over the influential position of attorney general.
However, shortly before the 1985 ousting of Nimeri, Turabi and other leaders of the Muslim Brotherhood were imprisoned.
In the elections of 1986 the National Islamic Front (NIF), successor to the ICF, won the third largest number of seats.
In 1988 Turabi served first as minister of justice and then as minister of foreign affairs as well as deputy prime minister in a coalition government with the Umma party.
However, in early 1989 the NIF was ousted from the coalition under pressure from the army.
After the military takeover of June 1989, Turabi and fellow leaders were imprisoned again, but he soon joined Bashir's National Salvation Revolution (Ingaz) and played a crucial role in designing the new government's Islamic policies.
In 1996 Turabi was elected speaker of the National Assembly and in 1998 secretary-general of the NCP, which evolved out of the NIF. However, in 1999 he was ousted from these positions over differences with the government.
Since forming the PCP in 2001, he and party leaders were repeatedly arrested and placed under house arrest, yet they remained one of the most vociferous opponents of the ruling NCP.
He selected Abdallah Deng Nhial to run for president, saying that he wanted to show the PCP was a national party with no regard for race or ethnicity.
|Abdallah Deng Nhial - Popular Congress Party
Abdallah Deng Nhial, 56, is a south Sudanese Muslim who was part of Bashir's government before Turabi formed the opposition PCP in 2001. He is the PCP's presidential candidate.
He is from the largest southern Sudanese tribe, the Dinka, and is a relative of the late SPLM leader John Garang.
From a humble background in the south, he said he wants to reduce poverty by prioritising education, health and sanitation, and stamping out corruption.
He hopes that as the first south Sudanese president - he is the only southern candidate - he will encourage southerners to vote for unity in a 2011 referendum on independence.
From a multi-faith family of Christians, Muslims and traditional religions, he said his party would not enforce Islamic law on the south.
Nhial is an Arabic teacher and graduated from al-Azhar University in Cairo. He was minister of religious endowments, youth and sport, minister of peace and a parliamentary whip during his 10 years of government.
|Salva Kiir Mayardit, Sudan People's Liberation Movement
Born in 1951, Salva Kiir Mayardit is the current president of the autonomous Government of Southern Sudan and the successor to the post of vice president of Sudan, following the death of John Garang in a crash on 30 July 2005.
|Kiir is the president of southern Sudan and leader of the opposition SPLM [EPA]
A founding member of the rebel Sudan People's Liberation Army (SPLA), he was chosen by the SPLA leadership to continue the peace process that formally ended the Second Sudanese Civil War in January 2005.
He is from a village close to Sudan's north-south border in Warrap State, one of the most underdeveloped areas of the war-ravaged south. He is from the south's largest Dinka tribe, which critics say dominates southern politics and the army.
In the 1960s, Kiir had joined the southern rebels in the First Sudanese Civil War. By the time of the peace deal of 1972, he had become an officer in the rebel forces and found a position in the regular army.
When John Garang joined an army mutiny that he had been sent to quell in 1983, Kiir joined him to found the Sudan People's Liberation Movement (SPLM), and rose to head its military wing, the SPLA.
Besides maintaining a shaky peace with north Sudan, one of his major achievements was the successful integration into the southern army of a large militia of some 40,000 men, which during the war fought against his forces.
Kiir was involved in the early stages of negotiating the peace treaty that ended the civil war and is well-known to northern politicians.
His selection by the SPLM leadership to succeed Garang was seen by analysts as a clear signal that they intended to keep the peace process on course, despite Garang's unexpected death.
Some opponents say that he has failed to end corruption, create a respectable modern army or achieve peace between fractious tribal groups.
His refusal to run for the presidency of Sudan is seen as a sign of a desire on his part and on the part of SPLM to remain ready to split away and form his own state and government if the 2011 referendum leads to a "yes" vote for the south to secede from the north.
He says he prefers an attractive unity with the north but last year, Kiir has made increasingly separatist statements, giving credence to those who always said he was a secessionist.
|Yasir Arman - Sudan People's Liberation Movement
Yasir Arman, the SPLM's presidential candidate, is a northern Muslim who joined the former southern rebel SPLM 24 years ago.
|Arman is a northern Muslim and presidential candidate for SPLM in the south [Reuters]
He says his nomination proves the SPLM is a truly national party, and has vowed to win the votes of the millions of marginalised in Sudan, push through democratic reforms and prioritise development.
Some analysts say the SPLM's decision to nominate him, rather than party leader Salva Kiir, implies they are more interested in consolidating their position in the south than in winning the national poll.
Kiir is running in the separate poll for president of southern Sudan which is due to vote on independence in 2011.
Arman, 49, whose father is from the same Ja'aliy tribe as Bashir, has been vilified by the NCP.
As the head of the SPLM parliamentary group, he advocated that Islamic law not be applied to non-Muslims, resulting in some Islamic scholars issuing a fatwa implying Arman was an apostate, a crime punishable by death.
He is married to a Christian Dinka from Abyei and has two daughters. Arman was nominated with more than 56,000 supporting signatures for the presidency.
|Sadeq al-Mahdi - Umma Party
Sadeq al-Mahdi, 74, is the leader of the Umma party.
|Mahdi is leader of the Ansar religious sect that has a huge following in Sudan [AFP]
He is revered by a large part of Sudan's northern population as a spiritual leader and a descendent of the self-proclaimed Mahdi, a visionary religious figure who fought against the British occupation in the 19th century.
In the elections, Mahdi will rely on his democratic credentials as Sudan's last elected civilian prime minister and on the large support for his party's associated Islamic sect, the Ansar.
Oxford educated, he served as prime minister twice before being overthrown by Bashir in 1989. His party has suffered splits since his return from exile in 2000.
He was imprisoned until 1991 and he left the country on his release.
The Umma traditionally enjoyed mass support in Darfur. Late last year, he was one of the driving forces behind the loose "Juba" alliance between more than 20 parties, including the SPLM, the Communists and the PCP.
The "Juba Alliance", which called for democratic and financial reforms, has since shown signs of faltering. Its members have hinted they would rally behind a single candidate against Bashir if there is a second round of the presidential poll.
|Mubarak al-Fadil al-Mahdi - Umma Reformation and Renewal
Fadil al-Mahdi, 59, is a cousin of Sadeq al-Mahdi and former member of his Umma party who served as interior minister before the coup of 1989.
After the military takeover he went into exile in London. He was instrumental in creating the National Democratic Alliance (NDA) and became its secretary general.
In 1994 he signed the Chukudum agreement that integrated the SPLM into the NDA.
When the Umma Party left the NDA in 1999, Fadil al-Mahdi returned to Khartoum. He split with Sadeq in 2002 and founded his own splinter faction of the Umma party, Umma Reformation and Renewal (URRP) and joined the government.
Fadil al-Mahdi became assistant president and a number of his fellow URRP activists were appointed to government positions.
However, in 2004 Fadil al-Mahdi was ousted because of his criticism of the government’s policy in the Darfur and Eastern Sudan.
In 2007 Fadil al-Mahdi, his secretary general Abdel Jalil Basha and other URRP politicians were imprisoned on allegations of a planned coup.
|Mohamed Ibrahim Nugud - Sudanese Communist Party
Mohamed Ibrahim Nugud, 79, is the head of the Sudanese Communist Party that was founded in 1946. He has been involved in politics since the early 1950s and has spent almost all his political career working underground.
He was elected as a member of parliament in 1965, and then went into hiding from 1971 to 1985 and was arrested in 1989. In 1990 he was released under house arrest until 1994 and then again went into hiding inside Sudan till 2006.
He has held the position of Secretary General since 1972. Many ex-Communist Party members criticised him for slowing down the process of change and political direction of the party and stifling free debate within the party institutions.
He struggled throughout his life within the party for the creation of a secular state with special focus on solutions for social problems.
"We are still committed to our Marxist orientation. We think Marx's analysis of capitalism in the 19th century was useful and we use his methods as a tool to examine the current situation. We are advocating socialism in a multi-party system," he recently said.
|Lam Akol, Sudan People's Liberation Movement - Democratic Change
Lam Akol, 59, is the leader of the Sudan People's Liberation Movement - Democratic Change (SPLM-DC).
|Akol broke away from the SPLM to form his own political party [AFP]
He is a prominent member from the Shilluk tribe and was born in a small village in the oil-producing Upper Nile State.
A southern intellectual with a PhD in chemical engineering, he was a lecturer in Khartoum when Sudan's second north-south war broke out in 1983. He also worked recruiting people for the southern insurgency.
In 1991, he and the southern rebel commander Riek Machar, now the south's vice president, split from the southern rebels complaining that its leadership was undemocratic and that there had been an unnecessary loss of life.
The split triggered the most demoralising period of the war for many southerners in which tens of thousands of people lost their lives in south-south battles.
His armed group controlled parts of Upper Nile State and in 1997 he signed the Fashoda Peace Agreement with Khartoum. However, he later returned to the southern rebel SPLM.
He was given a prominent job in the coalition national government formed after the 2005 peace deal. Many in the SPLM complained that as Sudan's foreign minister, he was too closely aligned with the north and he was removed.
The SPLM says his SPLM-DC party is funded by Khartoum, which he denies.
Akol is promising an end to corruption in his campaign which has been limited in the south, which his party says is because of harassment by the SPLM-dominated authorities.
While many analysts believe he is unlikely to win, he may attract votes from those fed up with greedy south Sudanese government officials.
Suliman Arcua Minnawi, known as "Minni", was born in 1968 in Furawiyya, North Darfur. He is the leader of what once was the largest faction of the Sudanese Liberation Army (SLA) until it was weakened by dissention and infighting.
A former school teacher, Minnawi was the secretary of SLA leader Abdul Wahid Nur, before the organisation split in 2004.
He's the only Darfur rebel leader to sign a peace agreement with the Sudanese government, in 2006. By the terms of that agreement he was appointed presidential advisor to Bashir and at the same time head of the Darfur Transitional Authority.
However, Minnawi's much criticised deal among other rebel leaders has not been fully implemented on every aspect of it. His militias have not been integrated into the Sudanese army as yet.
He still holds his own territory in Darfur, constantly complains about the government's violation of the peace agreement and its reluctance to fully implement it.
The government accuses Minnawi on the other hand of maintaining secret ties with other rebel factions and conniving with them against the regime.
Minnawi is from the Zagawa, one of the largest tribes in Darfur. They straddle the border with Chad and some analysts say they played a key role in importing weapons and lawlessness from the neighbouring country.
His movement has been trying to get approved as a political party but that has not yet materialised due to differences with the government over the implementation of the peace agreement.
However Minnawi has chosen 200 candidates from his movement to run for different positions during the upcoming elections including the positions of governors in Darfur's three regions.
|Khalil Ibrahim – Justice and Equality Movement (Jem)
Khalil Ibrahim is from the Koba branch of the Zagawa ethnic group, which is located mainly in Sudan, with a minority on the Chad side of the border.
|Ibrahim, who led an attack on Khartoum in 2008, is said to be close to Turabi [EPA]
He was an enthusiastic supporter of the National Islamic Front (NIF) seizure of power under the direction of Islamist Hassan al-Turabi in 1989, but was later part of a covert cell of Islamists who sought to change the NIF from inside.
He served as the state minister for education in Darfur between 1991 and 1994 in al-Fashir, North Darfur, and as the state minister for social affairs in Blue Nile in 1997 before a post as advisor to the governor of Southern Sudan in Juba in 1998.
In December 1999, when Bashir sidelined Turabi, Ibrahim was in the Netherlands, studying for a Masters in Public Health at the University of Maastricht.
As leader of the Justice and Equality Movement (Jem), he led a brazen attack on the Sudanese capital, Khartoum, in May 2008 that is alleged to have been backed by Sudan.
Since then he has been part of peace talks which lead to the signing of a framework agreement in Qatar during March 2010.
Ibrahim is from the Zagawa tribe like Minnawi but his movement is not essentially tribal or ethnic, but is based on the Islamic Brotherhood ideology which unites adherents from different ethnic backgrounds. He is said to be close to Turabi.
However he is supported by the Chadian president Idris Debby who also belongs to the same tribe on the other side of the border.