Gary Oldman thinks his performance in the 'Harry Potter' movies was "mediocre".

The 65-year-old actor joined the wizard franchise for the third film playing Harry's godfather Sirius Black in 2004's 'Harry Potter and the Prisoner of Azkaban' and reprising the role in three more movies, but Oldman has now admitted he's not proud of his portrayal of the character.

During an appearance on Josh Horowitz's 'Happy Sad Confused' podcast, Oldman explained: "I think my work is mediocre in it."

Oldman said he wishes he'd taken the time to read J. K. Rowling's books on which the films were based like his late co-star Alan Rickman - who played Professor Severus Snape - because it would have changed the way he portrayed Sirius Black.

He added: "Maybe if I had read the books like Alan, if I had got ahead of the curve, if I had known what's coming, I honestly think I would have played it differently."

Oldman went on to joke his character was killed off too early, adding: "We [the cast] were all taking bets [on which character would die], you know, it’s Hagrid, and I was there going, no, no, no, maybe it’s Ron. And then you kind of open the script and you go, it’s me. I’m out of here."

During the podcast, the actor insisted he's often overly-critical of his own work but he thinks that's a good thing.

He explained: "I’ll tell you what it is. It’s like anything, I think if I sat and watched myself in something and said, ‘My God, I’m amazing,’ that would be a very sad day, because you want to make the next thing better ...

"It’s so subjective. It’s such a personal thing that you’re looking at that other people are not seeing … It’s not to disrespect someone who says to me, ‘Oh, I really love you in that movie,’ and I’m thinking, ‘I’m terrible in that movie. What are they talking about?’ It’s not that. It’s [that] they’re seeing something else."