Once described as "Britain's number one terrorist", Sinn Fein's Martin McGuinness played a major role in Northern Ireland's peace process.

Widely accepted as a one-time IRA Chief of Staff, McGuinness (66) moved from his 'army' role to successfully share political power with one of his deadliest enemies.

Not alone did he share power with anti-republican DUP leader Ian Paisley, the two got on so well together they were dubbed the 'Chuckle Brothers'.

When he left school in Derry at 15 he experienced sectarianism first hand when he was rejected for a job as a mechanic because of his Catholic religion.

His determination to fight the republican battle solidified when Seamus Cusack (28) and Desmond Beattie (19) were shot dead by soldiers in Derry on the same day in July 1971.

Although a former teacher had described McGuinness as a well-mannered student who was "not outstanding in any way", he found his calling as a focused IRA activist.

His reputation grew. During the 16 months up to December 1972 a total of 26 British soldiers were killed by the Provisional IRA in Derry.

Years later McGuinness said: "I was proud to be a member of the IRA. I am still - 40 years on - proud that I was a member of the IRA.

"I believed that in a situation where the community that I came from were being treated like second and third-class citizens that I had a responsibility to fight back against it. And I don't apologise to anybody for having done that. I think it was the right thing to do."

In July 1972 McGuinness was part of a seven-member IRA delegation flown to London to meet Northern Ireland Secretary William Whitelaw to try and end the Troubles. These talks were unsuccessful.

The following year the Special Criminal Court in Dublin sentenced McGuinness to six months in prison for IRA membership. He had been caught in a car containing large quantities of explosives and ammunition.

He refused to recognise the court and declared his membership of the IRA.

His switch to politics came in 1983 when he contested elections to the House of Commons. He was finally elected in 1997, after three failed attempts, to represent Mid Ulster.

McGuinness refused to take the seat in line with Sinn Fein party policy as it would have involved swearing an oath of allegiance to the Crown.

He was re-elected to the seat in 2001, 2005 and 2010.

In the 1990s the Cook Report on ITV claimed that he was "Britain's number one terrorist", fuelling unionist calls for Sinn Fein to be banned.

He and other Sinn Fein figures responded with a series of counter-attacks on the Cook Report.

During the 1990s he was the IRA's chief negotiator in secret talks that ultimately brought about the Good Friday Agreement in 1998 that largely ended the Troubles.

McGuinness was later appointed Education Minister in the new Assembly.

One of his first decisions was to eliminate the controversial 11-plus examination which he himself had failed 38 years previously.

The Assembly was suspended after disagreements over issues such as policing and the decommissioning of IRA arms but a new agreement was reached in 2006.

Sinn Fein and the DUP became the two largest parties in the assembly and formed a coalition.

McGuinness was appointed Deputy First Minister with DUP leader Ian Paisley as First Minister.

The two bitter enemies became firm friends and after Paisley's death in 2014 his wife Eileen revealed that McGuinness had been very supportive to her family.

When Paisley retired in 2008, McGuinness worked as Deputy to First Minister Peter Robinson, who was considered to be even more anti-republican than his predecessor.

In 2010 McGuinness stepped down from his Assembly post to run in the Presidential election in the Republic.

When he finished third in that race, he returned to the Assembly within days.

But his relationship with Arlene Foster, who took over as First Minister in 2015, has been far more strained.

Foster spoke of her difficulties with McGuinness because he delivered a graveside oration for the IRA man she believed tried to murder her father.

She said however she would still work with McGuinness as "the past is the past".

He has never let go of his view that Ireland would be united. "I believe a united Ireland is inevitable. Absolutely, but I believe it can only happen by peaceful and democratic means," he said.

The contenders

While Sinn Fein does not intend to immediately nominate a replacement for Martin McGuinness, the party has plenty of choices for the next Deputy First Minister.

Newry and Armagh MLA Conor Murphy is viewed as a favourite. If the party still views former IRA members as leadership material, he will be a contender. He has also worked alongside Arlene Foster in the same office building and they got on well.

If IRA links are not viewed as desirable, Finance Minister Mairtin O Muilleoir is clever and charismatic. The media savvy businessman has a high profile on Twitter.

Another heavy hitter is former minister John O’Dowd. He took over as Deputy First Minister from Mr McGuinness during the 2012 Irish presidential election, and has no IRA record.

Belfast Telegraph