By David Thompson
Political Correspondent, BBC News
Mr Cairns has been an MP since 2001
On the face of it, David Cairns - who has quit the government after calling for a challenge to Gordon Brown - makes an unlikely assassin.
A former Catholic priest, who was given a leg up the ministerial ladder by the prime minister himself, his resignation is further proof, if any were needed, that politics can be a brutal business.
The Greenock and Inverclyde MP is hardly a household name but he is a popular figure with colleagues and his departure will be a blow to Mr Brown, as it keeps the issue of his leadership in the headlines ahead of this weekend's Labour conference.
Before his dramatic resignation, Mr Cairns was probably best known for getting the law banning former priests from entering Parliament changed.
He had been selected for the safe seat of Greenock and Inverclyde, but was ineligible to sit in the Commons until the 200-year-old Clergy Disqualification Act was reversed in 2001.
David Cairns was born and bred on the patch he now represents. All of his family live in the area and he is extremely proud that as a local man, he is the MP for the place where he grew up.
He was born in 1966 and was educated at the local schools. From 1991-94 he was an ordained priest in the Catholic church, having attended the Gregorian University in Rome and the Franciscan Study Centre in Canterbury. Mr Cairns worked in parishes in Scotland and south London, but found increasingly that politics was becoming his passion and decided he wanted to work for the Labour Party.
His political career started in 1994 when he became director of the Christian Socialist Movement.
He was also a councillor in the London Borough of Merton and - interestingly - worked as a researcher for one of the local MPs, Siobhan McDonagh, the junior Whip sacked for calling for a leadership contest.
His Westminster career began in 2001 when he became the MP for Greenock and Inverclyde, taking over from Norman Godman after he retired.
His first step on the ministerial ladder came two years later, when he was made Personal Private Secretary (PPS) to Malcolm Wicks, then pensions minister.
In 2005, he was elected as MP to the new seat of Inverclyde and became a junior minister at the Scotland Office. In 2007, he was promoted to become a Minister of State at the department, in effect, looking after the Scottish brief, allowing Des Browne, the Scottish Secretary, to devote time to his other post as Defence Secretary.
David Cairns' interests include football, cinema and US history.