- Ten-second biography
Was deputy political secretary to Tony Blair during his first term as PM before becoming an MP in 2001. Ran for the deputy leadership in 2007, topping the first round of the contest but coming third overall. Reported to have turned down a government job offered to him by Gordon Brown last year.
- What is his background?
The son of a sailor, Cruddas has made much of his working-class roots. Educated at a Catholic comprehensive near Portsmouth and gained a PhD at the University of Warwick before he began his political life as an assistant to two Labour general secretaries in 1994. Later moved to Downing Street to be the link between government and the trade unions.
- Where does he sit politically?
He is seen as on the left of the party and has rebelled against the Government over the imposition of university tuition fees. But Cruddas is not the extreme left-winger that some suggest - for all his differences with New Labour he has voted for the Iraq war, the abolition of the 10p tax rate and the 42 days law.
- Why he is one to watch
Cruddas is widely expected to do well in any Labour leadership contest. He is seen as the most high risk, high reward choice of leadership contenders.
- Something you might not know
Cruddas' wife was a special adviser to the late Mo Mowlam.