Matt O'Connor is perhaps best known as the founder and spokesman for the controversial campaigning group Fathers 4 Justice.
Members of the group made the headlines throughout 2004 for a series of high-profile stunts, including hurling purple powder at Tony Blair in the Commons and a Buckingham Palace protester in a Batman costume.
Mr O'Connor announced it would disband after reports linking it to a plan to kidnap Tony Blair's son Leo - he said "extremist elements" had undermined the group's credibility. However some members have continued to stage protests.
The marketing and design consultant has since written a book on the story behind Fathers 4 Justice and was in the process of setting up his own political party, the People's Alliance, when he was approached by the English Democrats to run for them in the mayoral contest - after media pundit Garry Bushell pulled out.
Mr O'Connor told BBC London: "We were engaged in a conversation and it sort of came up. As far as I was concerned they had already done a lot of the leg work in terms of what I was going to be doing anyway."
The English Democrats aim to restore what they see as the imbalance between England and the rest of the UK - from funding via the Barnett formula to the West Lothian Question.
But Mr O'Connor said he would not just be "banging on about the English Parliament". He sees himself as a "battered everyman" who understands the way people live and is not afraid to take on "big government" to defend people's liberties.
Born in Manchester in 1967 into a Labour-supporting family, Mr O'Connor regularly went out canvassing for the party and says he was among activists supporting Cherie Blair's unsuccessful bid for the seat of North Thanet in 1983.
He has also been a member of the Fabian Society, CND, Amnesty International, and says he gained experience of direct action in supporting the miners' strike and taking part in anti-apartheid protests.
He founded Fathers 4 Justice after a difficult divorce left him struggling to maintain contact with his children - although the problem had been resolved by the time the group was up and running.
Its high-profile, often controversial, campaign highlighted calls for improved rights for men denied access to their children.