Sinn Féin's Martin McGuinness, Northern Ireland's former deputy first minister, has died aged 66, reports BBC.
It is understood he had been suffering from a rare heart condition.
The former IRA leader turned peacemaker worked at the heart of the power-sharing government following the 1998 Good Friday Agreement.
He became deputy first minister in 2007, standing alongside Democratic Unionist Party leaders Ian Paisley, Peter Robinson and Arlene Foster.
McGuinness stood down from his post in January in protest against the DUP's handling of an energy scandal, in a move that triggered a snap election. Sinn Féin president Gerry Adams said: "Throughout his life Martin showed great determination, dignity and humility and it was no different during his short illness.
"He was a passionate republican who worked tirelessly for peace and reconciliation and for the re-unification of his country. But above all he loved his family and the people of Derry and he was immensely proud of both."
Prime Minister Theresa May said although she could never "condone the path he took in the earlier part of his life, Martin McGuinness ultimately played a defining role in leading the republican movement away from violence".
"In doing so, he made an essential and historic contribution to the extraordinary journey of Northern Ireland from conflict to peace," she added.