Former Irish taoiseach (prime minister) John Bruton says that despite "profound political differences" he always found Martin McGuinness to be a "very friendly person and easy to talk to". 

"The good and warm personal relationship he developed with Ian Paisley set a very good example. But it has yet to be followed by a genuine political reconciliation between the two communities they represented.

"It is sad that Martin will not be around to complete the important task he undertook."

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Image source, PA

Alastair Campbell, former UK Prime Minister Tony Blair's top aide during the time of the peace process, says he liked Martin McGuinness from the moment he met him.

There was something about him that was very, very special, he says. 

"I liked his toughness, his wit - he was actually a very warm human being who I grew to be very fond of."

He says he thought he had genuinely changed and, as a result, he was able to lead a movement to change.

From their last conversations, Mr Campbell says he knew Mr McGuinness was really worried that the peace process was in danger of going backwards.

The mayor of Martin McGuinness' home city of Derry (pictured) pays tribute to a "towering figure in Northern Ireland in general and in the city of Londonderry in particular". 

Hilary McClintock, a DUP councillor, says: "Whilst there will continue to be a diverse range of opinions on Mr McGuinness' contribution to society over his lifetime, it is clear that he had a passion for the city and the wider north-west area."

Former Ulster Unionist MP, Lord Kilclooney, told the BBC: "As a victim of IRA assassination attempt when I was Minister at Home Affairs in Northern Ireland in 1972, I obviously watched the political progress of Martin McGuinness closely. He had an evil past but became a peacemaker - of that I have no doubt."

The peer added: "I extend my condolences to his family circle at this time but I look in despair at Sinn Féin for someone with the same leadership qualities as Martin McGuinness".

The Queen's two-day visit to Northern Ireland in 2012 was marked by an historic handshake . 

Her Majesty and former IRA commander Martin McGuinness shook hands for the first time.

The meeting between the monarch and Northern Ireland's deputy first minister took place at a charity event in Belfast.

Image source, Pacemaker

We take a look here at the career of Martin McGuinness in pictures.

Peace campaigner Jo Berry reacts to Lord Tebbit's comments (see 09:13 post) that Mr McGuinness was a coward and only became a man of peace so he could avoid murder charges.

Traditional Unionist Voice leader Jim Allister has said all families deserve condolences after a death but added that Martin McGuinness "lived many more decades" than most IRA victims.

Image source, Empics

"Sadly, Mr McGuinness thought it appropriate not just to sanction and commit murder but to take those dark secrets to his grave, denying truth and justice to many IRA victims. So, today my primary thoughts are with the many victims of the IRA who never reached the age of 66," Mr Allister added.

George Hamilton, the chief constable of the Police Service of Northern Ireland (PSNI), says that "many police officers and their families are among those who suffered" during the Troubles but that Martin McGuinness  "believed in a better future for our community, and this is a vision shared by policing". 

"Martin's journey in life challenges all of us who care about the future; to be prepared to change; to demonstrate leadership; and to work to understand the world, not just from our own perspective, but from the perspectives of everyone in our community," he says. 

James Martin Pacelli McGuinness was born into a large family living in the deprived Bogside area of Londonderry on 23 May 1950. His unusual third name was a tribute to Pope Pius XII.

He attended Derry's St Eugene's Primary School and, having failed the 11-plus exam, he went to the Christian Brothers technical college, known locally as Brow o' the Hill.

Image source, PA

He did not enjoy his time at college and his failure to qualify for grammar school rankled.

"It is my opinion," he later said, "that no education system has the right to tell any child at the age of 10 and 11 that it's a failure."

Read  more on the life of Martin McGuinness here .

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Julie Hambleton, whose sister, Maxine, was one of the 21 people killed in the Birmingham pub bombings in 1974, says: “Like every other family, Martin McGuinness has a family and they have our condolences.

“However, Mr McGuinness was very fortunate because he was able to live a full life unlike my sister, unlike 20 other victims and unlike so many other thousands of people who were murdered.

“With his death, the truth is buried."

She adds: "And this is something that needs to be tackled where Gerry Adams needs to now step up and speak the truth to give the honour to those families of the unknown, Disappeared, and so many others, even us, and tell us who murdered our loved ones once and for all.”  

Image source, Press Eye

Reaction is pouring in after the death of Martin McGuinness - we'll be continuing to report live here throughout the day, but if you want to read what has been said about the former NI deputy first minister in one place, then head over to our reaction page . 

Former DUP minister Jim Wells tweets: "My thoughts are with the families of Joanne Mathers, Patsy Gillespie, Frank Hegarty and all the other victims of the IRA in Londonderry."