A 57-year-old nephew of Saudi's King Salman, Mohammed bin Nayef bin Abdulaziz Al Saud was crown prince until he was replaced by his cousin, Mohammed bin Salman, as heir to the throne.
In a major Saudi hierarchy reshuffle on June 21, the former crown prince was also relieved of all his roles, including deputy prime minister and interior minister.
"I am content," Prince Mohammed bin Nayef said about his cousin's appointment to crown prince, adding: "I am going to rest now. May God help you".
With years of experience in intelligence work, and having played a major role in Saudi's internal security policies, Mohammed bin Nayef has been called "the prince of counterterrorism".
Analysts argue that Mohammed bin Nayef was also the most pro-American of the Saudi leadership, who, unlike his father, led the battle against al-Qaeda.
He attended school in the United States, taking classes at Lewis & Clark College in Portland, Oregon. In the late 1980s, Mohammed bin Nayef studied at the Federal Bureau of Investigation (FBI) before succeeding his father's position at the Interior Ministry. He also took "anti-terrorism" courses at the Scotland Yard Unit.
Before the September 11 attacks in the US, Mohammed bin Nayef had already developed a relationship with US officials as a respected figure in the "war on terrorism".
He led a crackdown on al-Qaeda in Saudi Arabia between 2003 and 2007, where attacks against security headquarters, foreign residential compounds and government buildings killed dozens of security officers and foreigners.
While leading Saudi's war on al-Qaeda, Mohammed bin Nayef was outspoken in the media, appearing frequently on TV to speak about the kingdom's manhunt of hardline operatives.
The US Central Intelligence Agency (CIA) regarded Mohammed bin Nayef as the key to defeating al-Qaeda.
George Tenet, former director of the CIA, described Mohammed bin Nayef as the agency's "most important interlocutor".
In 2009, Mohammed bin Nayef survived an assassination attempt by al-Qaeda after agreeing to meet Abdallah Asiri, a member of al-Qaeda who framed himself as a repentant former fighter. During the meeting in Jeddah, Asiri detonated a suicide vest, but ended up only slightly wounding Mohammed bin Nayef.
Since then, Mohammed bin Nayef has remained tough on internal security. There have been many arrests of suspected al-Qaeda and, more recently, of ISIL members since. His survival of the assassination attempt led many in Saudi Arabia to regard him as a hero.
He was appointed interior minister in 2012 and deputy prime minister in 2015, after which he transitioned into a more low-profile role, as Mohammed bin Salman, the newly crowned prince, built more a prominent role for himself as the architect of the Yemen war.
In 2017, Mohammed bin Nayef was awarded a medal by the new director of the CIA, who honoured his contributions to "counterterrorism" work.
Source: Al Jazeera and news agencies