Gary Oldman claims playing Sirius Black in the Harry Potter movies has made him a "cool dad".The critically acclaimed actor - who has reprised his role as Harry's godfather for the fourth movie in the adventure series 'Harry Potter and the Order of the Phoenix' - says his two children think he is incredibly hip for starring in the last three movies of the successful franchise. Gary, 49, told Empire magazine: "I like the character because he is unpredictable, and very volatile, but he isn't a bad guy."But I also liked the dynamic that he was set up to be a bad guy, and was actually something quite different. And of course I've got kids of my own now, and they love me being in the Harry Potter films."I'm now part of a phenomenon. You become incredibly cool to your kids, and you get a young fan base. So you became the cool dad at school. You're suddenly hip."The star also revealed he has formed a close friendship with Daniel Radcliffe, who stars in the title role. He added: "The kids in the movies are excellent, and in some ways it's the closest thing to theatre, because there's that sense of the company."And you become close and don't all drift away like you do after most films.The people working on it are so good, and Dan in particular has become a good friend. We've become quite close."