From BBC News: Christopher Eccleston, who is about to star in BBC Four biopic Lennon Naked, took on the role of the Time Lord when Russell T Davies revamped Doctor Who in 2005.
He told the Radio Times he was proud of the show but "wasn't comfortable" working on it. "I think it's more important to be your own man than be successful, so I left."
Eccleston, the ninth Doctor announced he was leaving after just one series to be replaced by David Tennant.
"I was open-minded but I decided after my experience on the first series that I didn't want to do any more," he said.
"I didn't enjoy the environment and the culture that we, the cast and crew, had to work in.
"I thought if I stay in this job, I'm going to have to blind myself to certain things that I thought were wrong."
But the 46-year-old said the fact that he played the Doctor - and not that he had quit - was "the most important thing".
"I really feel that because it kind of broke the mould and it helped to reinvent it.
"I'm very proud of it."
In an initial statement announcing his exit in March 2005, the BBC said the actor was afraid of being typecast and had found the series gruelling.
The corporation later accepted the statement was incorrect and that it had not spoken to Eccleston before releasing it.
"They handled it very badly but they issued an apology and I dropped it," he added.