Northern Ireland's new first minister Ian Paisley (L) and deputy first minister Martin McGuinness smiling after being sworn in at a ceremony at Stormont, Belfast May 8, 2007.  [Photo/Agencies]

He told a government inquiry that he had left the IRA military to work as a leading figure in Sinn Fein, the IRA’s political wing, in 1974, forming a close relationship with Gerry Adams, the charismatic republican from Belfast who has consistently said he was never an IRA commander, working only in Sinn Fein.

The two were the lead negotiators for the Republican movement, under talks initiated by US special envoy George Mitchell, chosen by then President Bill Clinton.

Tony Blair, the British Prime Minister at the time, paid tribute to McGuinness, saying: “I came to know the Martin McGuinness who set aside that armed struggle in favor of making peace. There will be some who cannot forget the bitter legacy of the war. And for those who lost loved ones in it that is completely understandable. But for those of us able finally to bring about the Northern Ireland peace agreement, we know we could never have done it without Martin’s leadership, courage and quiet insistence that the past should not define the future."

British Prime Minister Theresa May said Mr McGuinness “played a defining role in leading the Republican movement away from violence".

She added: “In doing so, he made an essential and historic contribution to the extraordinary journey of Northern Ireland from conflict to peace."

But perhaps the most obvious example of the road McGuinness travelled came when he met the Queen, the first of several meetings which included a 20-minute private audience not long before he retired as deputy first minister.

The meeting was all the more extraordinary because an IRA splinter group had been responsible for the murder of Lord Mountbatten, a World War II hero, last Viceroy of India, and a cousin of Queen Elizabeth.

He and his grandson, along with two others, were killed by a bomb placed in their fishing boat in Sligo, Ireland in 1979.

For many, the meeting of the monarch and the Republican marked the end of a bloody chapter of history in Northern Ireland.

Britain's Queen Elizabeth shakes hands with Northern Ireland deputy first minister Martin McGuinness, watched by first minister Peter Robinson (C) at the Lyric Theatre in Belfast June 27, 2012.  [Photo/Agencies]