When it was announced that I was doing this movie, I was a superstar overnight at my kids' school 
Gary Oldman and Michael Gambon are newcomers to Hogwarts in the third Harry Potter movie. Oldman plays the menacing Sirius Black, the titular Prisoner Of Azkaban, whilst Gambon steps in for the late Richard Harris to play Harry's headmaster, Professor Albus Dumbledore.
Were you influenced by any cinematic bad guys when you were a kid, and what were your children's reactions when they found out you were going to be in a Harry Potter movie?
Gary Oldman: I can't say I'm influenced by other bad guys - maybe Bela Lugosi - but I didn't really have a role model for this one. But when it was announced that I was doing this movie, I was a superstar overnight at my kids' school. Now they've got the posters and the t-shirts and the 'articulated action figure' of Sirius Black, so they actually take me to school on their share day. They're loving the whole experience. One of them is still a little young - Charlie, he's five - but my big boy Alfie, he's 15, and he was at the premiere. They're thrilled that I'm part of this family and this phenomenon that is Harry Potter.
How was it coming into this established family, and into an established role?
Michael Gambon: Well I knew most of the other actors anyway - I've known Maggie Smith for around 40 years, so I was quite relaxed with them. The first week was a bit tense, but then I settled down and did my own thing. What put me off was having to do a 25 word description of my character for Alfonso... I said "Did you ask Richard Harris to do that?" and he said "No."
GO: I arrived from a different planet, and I was intimidated. I knew that Dan [Radcliffe, Harry Potter] was a fan, and so you have the added responsibility of hoping that you live up to that expectation - I didn't want to disappoint him. I just wanted to do the best Sirius Black I could do. You are made to feel at home very quickly, but at first you are very much an outsider coming into this family.
Can you remember any of your school masters that were influential on you?
GO: I can't think of a single one. My kids - it amazes me - they love going to school. It actually excites them, going to school, and to me it was like being banged up every day. It was like prison. In a way, I'm grateful, through acting that that is the gift I've given them. But I haven't got a single good memory of school.
MG: I can't think of anyone. I hated them all and wanted to get out. My only memories of school are of being beaten, of being hit in the playground, of masters poking their fingers in my chest all day.
You've added something of yourself to the role. How hard is it to strike the balance without compromising the character of Dumbledore?
MG: It all happened with the costume, really. Richard was in heavy, heavy costume, he could hardly sit, you know, and I turned up and they put me in two layers of silk, so I played him much lighter - you know, floating around in a pair of slippers, a bit of a hippy. I had a slight Irish accent - because, you know, I am Irish - it sort of just happened. Alfonso asked "What accent are you using?" and I said "I'm not sure yet". So the Irish came out. He said, "What is that?" I said Irish, and he said he'd never heard it before.
