Sinn Fein's Martin McGuinness, a key figure throughout five decades of conflict and peace in Northern Ireland, says he's bowing out of politics and will not lead his nationalist party into elections in March.
The 66-year-old former IRA commander said illness and the current political crisis, triggered by his own resignation this month as Deputy First Minister, had led to him to step down several months earlier than planned.
He signalled that party president Gerry Adams was also preparing to make way for a successor.
The departure of the pair, key players in Northern Ireland's 30 years of Protestant-Catholic 'Troubles' and in forging the 1998 Good Friday peace agreement that largely ended them, would mark a generational change in Sinn Fein.
The party remains committed to breaking with Britain and uniting with the Irish Republic, though that is anathema to Northern Ireland's majority Protestants.
"Last year, Gerry Adams and I confirmed that we had a plan in place for transition to a new leadership. For my part, it was my intention to step aside in May this year," Mr McGuinness said in a statement.
"Unfortunately, my health and the current crisis have overtaken this time frame. I am not physically able to continue in my current role and have therefore decided to make way for a new leader."
Mr McGuinness had been Deputy First Minister for a decade before quitting this month in protest at First Minister Arlene Foster's handling of a controversial green-energy scheme.
His resignation led to the collapse of the power-sharing government at Stormont, the seat of the Northern Ireland Assembly.
British Prime Minister Theresa May said Mr McGuinness moved the republican movement towards peace.
"He played a key role in moving the republican movement towards a position of using peaceful and democratic means," she said.
"I want to send him best wishes for his retirement.
"We will all continue to work to make sure that the people of Northern Ireland are able to live freely and in peace."
Mr Adams hailed him as a patriot and peacemaker as tributes flooded in from across the political spectrum.
He said he had been shocked by Mr McGuinness's recent appearance.
"Thank God he is looking a lot better since then and responding well to the treatment he is receiving. However, he does need to take time out to get better for himself, for his family and for our struggle."
He added: "Martin has said he wants to come back and be part of the process to end partition, build reconciliation, unite our people and achieve Irish unity.
"Give him the space to get better and increase our efforts so that when he returns the process of change has advanced."
Northern Ireland Secretary James Brokenshire said he was sorry the former deputy first minister would not be standing for another term at the Assembly.