Pushpa Kamal Dahal, 53, popularly known as Prachanda, is the leader of the Communist Party of Nepal (Maoist) or CPN.
Prachanda was brought up in Nepal's Chitwan district and was born in 1954.
Born into a high-caste but poor farming family, Prachanda was driven to politics by the extreme poverty he witnessed in rural Nepal.
His interest grew in the communist groups that emerged in Nepal during the late 1960s after the king (Gyanendra's father) banned political parties.
In 1986, Prachanda became general secretary of the CPN.
He also led the People's Liberation Army, the military wing of CPN. Prachanda launched CPN's Nepalese People's War on February 13, 1996, which killed thousands of Nepalis.
In 1990, he went undergound and pursued a decade of armed struggle.
He announced a ceasefire and signed up to peace in 2006, that lasted 90 days.
He has had trouble losing his image as a man of war.
His immediate family members are active in Maoist politics, with his wife and daughter holding seats in the constituent assembly.
Now the most powerful man in Nepal, he is set to lead a new government.
Prachanda is the face of a "New Nepal," a popular Maoist slogan.
Tear gas was used by police to disperse the crowd, many of whom were heard shouting anti-king slogans such as, "Gyanendra, thief, leave the palace".
The lowering of the royal flag at Kathmandu's main palace came after a late-night vote on Wednesday by Nepal's newly elected Constituent Assembly to abolish the monarchy.
Thousands marched, danced and sang in the streets of the capital after the vote, setting off firecrackers, waving hammer-and-sickle flags and denouncing King Gyanendra.
One of the final symbols of the monarchy disappeared as the royal flag, a red square decorated with a flag-waving lion, was removed.
The palace was replaced by Nepal's national flag, a red banner of two triangles adorned with a sun and moon.
The removal of the royal standard was "a decision by the government to show that Nepal is now a republic,'" said a palace official who spoke on condition of anonymity.
There was no immediate reaction from the 61-year-old former monarch who was forced to restore democracy after widespread protests against his royal dictatorship started two years ago.
The Maoists majority win in April elections sealed the fate of the Shah dynasty which dates to 1769 when a regional ruler conquered Kathmandu and united Nepal.
Gyanendra has 15 days to leave the palace and move to his large private residence in the city, or he will face the possibility of being removed by force.
The Maoists are struggling to form a government in a country where every major political party has been linked to killings since the start of the peace process.
In Washington, Evan Feigenbaum, the deputy assistant secretary of state, told reporters that the US would work with the Maoist-led government to encourage stability, democracy and peace in Nepal.
However, he declined to speculate on whether the former rebels will be removed from the US list of "terrorist" organisations.
"The degree to which we can work with anyone in Nepal will depend, very directly, on the degree to which they continue to embrace the political process and abandon violence," Feigenbaum said on Thursday.