Profile: Labour MP Tom Watson
Tom Watson was a relatively obscure figure, little known outside Westminster, until he took one of the starring roles in the interrogation of Rupert and James Murdoch in 2011, as a member of the Commons culture select committee.
Suddenly an MP who had seemed destined to be remembered as a foot soldier, a loyal lieutenant of Gordon Brown, who had served as a junior minister in the Labour government and played a minor role in the toppling of Tony Blair, was a hot property.
He was drafted into Labour leader Ed Miliband's top team as the man charged with organising the troops to secure an overall majority at the next general election.
He had an image makeover, co-wrote a pacy account of his hacking adventure - Dial M for Murdoch - and became a familiar figure on the rolling news channels.
His record as campaign chief was mixed - the party famously lost safe Bradford West to a resurgent George Galloway but scored other by-election victories along the way. He had just launched a grassroots campaign aimed at securing victory for Mr Miliband in 2015.
His downfall came in the wake of a row over trade union influence over Labour candidate selection.Blair 'plot'
A former trade union official himself, who once shared a flat with Unite leader Len McCluskey, he entered Parliament in 2001 as MP for West Bromwich.
After an initial stint in the whips office, he was sent to the Ministry of Defence, where he was credited with helping secure pardons for soldiers shot for cowardice during the First World War.
But in 2006, he resigned as a defence minister, calling for Tony Blair to quit in the interest of the Labour Party and the country - a move that hastened the then prime minister's departure from office.
He was accused of conspiring against Mr Blair with Gordon Brown when it emerged he had visited the then chancellor at his home in North Queensferry, Fife, shortly before stepping down.
Both men denied any plot, but many - inside and outside Labour - did not believe them.
Mr Watson maintains his decision to take a stand against Mr Blair put him in the media firing line, and the then editor of the Sun - and former News of the World chief - Rebekah Brooks, a friend and supporter of Mr Blair, was one of those with their fingers on the trigger.
When Gordon Brown took over as leader and prime minister in 2007, Mr Watson was brought back into government as a whip, and in 2008 was appointed minister for digital engagement.
In that role, he found a niche.McBride row
Known as an early adopter of social media, he was the first MP to have a blog and has described himself as "an apprentice nerd" for his love of all things technological.
But during this period Mr Watson also had another run-in with the media - including News International - when he was accused of being involved in the scandal surrounding a plot by Gordon Brown's spin doctor Damian McBride to spread smears about senior Tories.
- West Bromwich East MP 2001-present
- 2005-6: Government whip
- 2006: Defence minister
- 2007-8: Assistant government whip
- 2008-9: Cabinet Office minister
- 2011-present: Labour deputy chairman
- 2011-2013: Labour elections co-ordinator
The Mail on Sunday accused him of "encouraging" Mr McBride while the Sun published a cartoon of him under the headline "Mad dog was trained to maul".
Mr Watson subsequently won "substantial" libel damages from both newspapers in the High Court, which ruled the stories linking him to the plot were not true.
He resigned from his ministerial role in the wake of the McBride row for family reasons, he insisted - he wanted to take a step back from front-line politics and concentrate on his wife and children.
Hoping for what he called "a productive life as a backbencher", he decided to join the culture select committee to pursue his interests in sport and the arts.
But just two days after joining, the Guardian newspaper put phone hacking back on the agenda and the committee decided to investigate it - once again thrusting Mr Watson into the spotlight.
Unlike some of his Parliamentary colleagues, Mr Watson does not claim that his mobile phone was ever targeted - but he says the issue is still personal for him.'Unattributed briefings'
"The first thing News International did was try to have me removed from the committee," he claimed in 2011.
"I realised then that these people were never going away. Something had clearly gone wrong with newspapers and somebody had to get to the truth.
"There weren't many MPs who were prepared to do that for fear of being targeted, so I decided I had to do it.
"I wanna break you in half" is the title of one of the tracks of Tom Watson's favourite band, Drenge. That may come as no surprise to those who have been taken on by this heavyweight political bruiser over the years”
"People then started coming to me - whistle-blowers and victims - and I felt I had a responsibility towards them. I couldn't walk away."
A prolific Tweeter about politics, as well as his latest discoveries in music, film and video games, he has recently been plugging a little-known blues-rock band, Drenge, even managing to squeeze in a mention of them and the Glastonbury music festival in his resignation letter.
His Twitter profile says: "According to the Sun newspaper, Watson is a fundamentalist zealot who denounces any deviation from socialism. MP and author of a book on corruption by NewsCorp."
Ed Miliband - another former Gordon Brown ally - drafted Mr Watson into his inner circle in the aftermath of his 2011 culture committee grilling of Rupert Murdoch.
In his resignation letter, Mr Watson, the son of a union official and a social worker, who has two children with estranged wife Siobhan, said it was better for the "future unity" of the Labour Party that he went,
The Falkirk row broke out over the seat being vacated by Labour's Eric Joyce - the Unite union has been accused of hijacking the process to select a new candidate to replace him, and Mr Watson's office manager was the union's preferred candidate.
In his letter to Mr Miliband, Mr Watson said he was not quitting because of "unattributed shadow cabinet briefings around the mess in Falkirk... though they don't help".
He said some within the party had still not forgiven him for resigning as defence minister in 2006, but adds: "I fully accept the consequences of that decision and genuinely hope my departure allows the party to move on."
Not for the first time in his career, he said he wanted to speak out from the back benches on issues of personal interest.