Gerry Adams has led tributes to Martin McGuinness, describing him as a “passionate republican who worked tirelessly for peace and reconciliation and for the reunification of his country”.
The Sinn Fein president paid tribute to his lifelong friend, saying: “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 reunification of his country.
“But above all he loved his family and the people of Derry and he was immensely proud of both.
“On behalf of republicans everywhere we extend our condolences to Bernie, Fiachra, Emmet, Fionnuala and Grainne, grandchildren and the extended McGuinness family.”
During his time in office Mr McGuinness forged an unlikely friendship with then Democratic Unionist Party (DUP) leader Ian Paisley and the two earned the nickname the Chuckle Brothers.
A Twitter account in the name of Mr Paisley’s son Kyle said: “Very sorry to hear about the passing of Martin McGuinness. Look back with pleasure on the remarkable year he and my father spent in office together and the great good they did together.
“Will never forget his ongoing care for my father in his ill health.”
Mr McGuinness was described as a “great guy” by former Labour communications chief Alastair Campbell.
He tweeted: “So sad Martin McGuinness has died. Some will never forgive his past but without him there would be no peace. The man I knew was a great guy.”
President of Ireland Michael D Higgins led tributes from the Republic, saying Mr McGuinness’s death leaves a gap that will be hard to fill.
“The world of politics and the people across this island will miss the leadership he gave, shown most clearly during the difficult times of the peace process, and his commitment to the values of genuine democracy that he demonstrated in the development of the institutions in Northern Ireland,” he said.
Mr Higgins said Mr McGuinness made an immense contribution to peace and reconciliation in Northern Ireland.
Democratic Unionist leader and former Stormont first minister Arlene Foster said she offered “sincere condolences”.
“Today’s news will come as a shock to many people,” she said.
“First and foremost, Martin McGuinness was a much loved husband, father and grandfather.
“My thoughts and prayers are with his wife and the family circle at this very painful time of grief and loss.”
She said history would record differing views on Mr McGuinness but he had played a pivotal role in bringing the republican movement toward peace.
Good Morning Britain host Piers Morgan tweeted: “RIP Martin McGuinness, 66.”
In a later post, he compared Mr McGuinness to former president of South Africa and anti-apartheid activist Nelson Mandela, saying: “Both men renounced violence to forge peace. The comparison is valid.”