BELFAST: When former IRA commander Martin McGuinness shook the hand of Queen Elizabeth II on Wednesday, it will have been seen by many supporters of a united Ireland as a betrayal of everything he fought for.

But the historic act of extending a republican hand to the British monarch merely marks the latest stage in McGuinness' remarkable transformation from paramilitary to peaceful politician.

Now deputy first minister of Northern Ireland, McGuinness was a leading member of the Irish Republican Army during its bloody campaign against British rule of the province, in which 3,500 people died in three decades of sectarian violence.

To republicans, the queen is commander-in-chief of the army they saw as an occupying force.

McGuinness played a major role in establishing peace, negotiating the landmark Good Friday Agreement in 1998 and sharing power with Sinn Fein's one-time bitter foes, the Democratic Unionist Party (DUP), in Belfast.

The 62-year-old once described as a ruthless commander is now a statesman who rubs shoulders with prime ministers, presidents -- and monarchs.

He said ahead of the meeting that by shaking the queen's hand he would be “shaking the hands of hundreds of thousands of unionists”.

James Martin Pacelli McGuinness was born in 1950 in Londonderry, and became involved in the civil rights movement as a teenager. He joined socialists Sinn Fein, now the main Catholic republican party, in 1970.

He became a member of the IRA and had risen to its second-in-command in Derry by the time of “Bloody Sunday”, the notorious day on January 30, 1972, when 13 unarmed civil rights protesters were shot dead by British soldiers.

Although McGuinness escaped detention by the British in Northern Ireland, he was jailed in the Republic of Ireland in 1973 after being caught with 250 pounds (113 kilogrammes) of explosives and 5,000 rounds of ammunition in a car.

At his trial, where he received a six-month sentence, he proudly declared his membership of the IRA, saying: “We have fought against the killing of our people. I am a member of Oglaigh na hEireann (the IRA) and very, very proud of it.”

Years later, in May 2001, after McGuinness became a politician, he spoke of his membership of the IRA with a level of honesty that few of his Sinn Fein colleagues have matched and which has removed some of the toxicity from his past.

McGuinness moved into politics relatively early, becoming one of five Sinn Fein members elected to the short-lived Northern Ireland assembly in 1982.

He was involved in secret talks with British officials between 1990 and 1993, and after the IRA ceasefire of 1994, became Sinn Fein's chief negotiator in the painstaking talks that led to the Good Friday peace accords.

When a power-sharing government was established in 2007, McGuinness was appointed deputy first minister.

To the amazement of many, he managed to work closely with First Minister Ian Paisley, the firebrand Protestant preacher who led the staunchly pro-British DUP until 2008.