Adams, who will turn 70 next October, has always denied membership of the IRA but accusations from former IRA fighters that he was involved in its campaign of killings have dogged him throughout his career.
Adams was a key figure in the nationalist movement throughout the three decades of violence between Catholic militants seeking a united Ireland, mainly Protestant militants who wanted to maintain Northern Ireland’s position as a part of Britain, and the British army.
3,600 died in the conflict, many at the hands of the IRA.
As head of the political wing of the IRA during its bombing campaigns in 1980s Britain, Adams was a pariah and banned from speaking on British airwaves, forcing television stations to dub his voice with that of an actor.
He and his party emerged from the political cold in October 1997 when he shook hands with Labour Prime Minister Tony Blair at their first meeting. A year later, he helped win sceptical elements in the IRA to the Good Friday peace deal, which largely ended the violence.
Since the peace deal Adams and McGuinness turned Sinn Fein from a fringe party into the dominant Irish nationalist party in Northern Ireland and the third largest party in south of the border.
While its anti-austerity platform led to a six-fold increase in its number of seats in the Republic – 23 out of 158 – suspicion of Sinn Fein’s role in the Northern Ireland troubles still runs deep and the far larger ruling Fine Gael and or main opposition Fianna Fail have ruled out governing alongside them.
Analysts say a change of leader could help open the way to Sinn Fein entering government in Dublin for the first time.
“Under a new Sinn Fein leader I think anything is possible,” said David Farrell, politics professor at University College Dublin.
A new Sinn Fein leader will also take over responsibility for rescuing power-sharing devolved government in Northern Ireland and avoid a return to full direct rule from London for the first time in decade.
Power-sharing collapsed after Sinn Fein withdrew in January saying the Democratic Unionist Party was not treating it as an equal partner and a series of talks have failed to break the impasse.