Tony Blair has disclosed how he was inspired to enter politics by the example of the Russian revolutionary Leon Trotsky.
The former prime minister, who remains a hate figure for many on the left, said that he had briefly been a "Trot" while at university at Oxford in the 1970s.
In an interview on BBC Radio 4's Reflections With Peter Hennessey, Mr Blair said his enthusiasm was fired after picking up a biography of Trotsky after performing at a gig with his student rock band Ugly Rumours.
"When I got back I picked it up and started to read it. And I literally didn't stop reading it all night. It opened a different world to me," he said.
"I suddenly thought the world's full of these extraordinary causes and injustices and here's this this guy Trotsky who was so inspired by all of this that he went out to create a Russian revolution and change the world.
"It was like a light going on.
"And even though over time I obviously left that side of politics behind, the notion of having a cause and a purpose and one bigger than yourself or your own ambition - and I think probably allied at the same time to coming to religious faith - that changed my life in that period."
Mr Blair said his enthusiasm lasted for about a year and was finally quenched when he began dating his future wife, Cherie Booth, while they were both training to be lawyers.
"She was a sort of mainstream Labour person then and remained that literally all the way through," he said.
"That was influential because obviously when we started going out together she was extremely critical of what she regarded as my sort of Oxford student socialism. So she made that very clear."
Mr Blair also disclosed how Gordon Brown - with whom he later feuded bitterly when they were both in government - helped him write his first Labour Party conference speech when they were both shadow junior ministers.
"It was a very, if I may say so, very intelligent analysis of what was wrong with Conservative employment law and how we were going to change it. But in terms of a conference speech, it plainly didn't work," he said.
"He said to me, 'Oh my god, you can't say this, it's ridiculous', and then literally sat down and wrote out the first opening lines.
"I remember thinking well, he knows more about it than me so I'm just going to go and give it, and then being absolutely astonished at the extraordinary reaction I got from the conference. And after that I thought, yeah, well that's obviously the way to do it."