Salva Kiir Mayardit became president of South Sudan - then still part of Sudan - and head of the Sudan People's Liberation Movement (SPLM) in 2005, succeeding long-time rebel leader John Garang, who died in a helicopter crash.
Mr Kiir was re-elected as president in multiparty polls in the south in April 2010. On South Sudan's independence in July 2011, he became president of the new state.
Prior to independence, he was also vice-president of Sudan, under the power-sharing arrangements put in place in the 2005 Comprehensive Peace Agreement (CPA).
During a historic first visit to Sudan since independence, Salva Kiir in October 2011 ruled out a return armed conflict between the new neighbours, despite continuing tensions.
He has also taken a tough line on corruption, and in September 2011 announced several measures to combat it, including plans to subject government contracts to procurement legislation and make officials publish their assets and earnings.
Having fought in the south's first civil war in the 1960s, Mr Kiir joined the Sudanese army after the 1972 peace agreement. He defected to the rebels again on the resumption of fighting in 1983, later emerging as the SPLM's military leader.
Born in 1951 in Bahr al-Ghazal state, he is a Christian and - like his, predecessor John Garang - a member of the Dinka, the largest ethnic group in South Sudan.
Although he lacks Mr Garang's charisma, Mr Kiir has enjoyed a reputation for integrity and was initially seen as being able to reconcile ethnic or political opponents.
In mid-2013 President Kiir sacked his entire cabinet, including Vice-President Riek Machar, in an apparent power struggle within the SPLM. As Mr Machar belongs to South Sudan's second largest ethnic group, the Nuer, some analysts saw the move as an indicator of increasing communal tension.
In December, President Kiir alleged that his former vice-president had instigated a failed coup. The accusation sparked clashes between rival army factions in which hundreds of people died. Government and rebels agreed to attend peace talks in Ethiopia in January 2014.