Sirius Black and James Potter attended Hogwarts together, and Sirius is Harry’s godfather. Sirius is an Animagus, which means he can transform himself into a black, shaggy dog named Padfoot at will. Years ago, Sirius was wrongly imprisoned at Azkaban for the murder of thirteen people. Following his escape, he has been forced to live in absolute secrecy. To keep Sirius safe, Dumbledore demands that Sirius not leave his parents’ home at Twelve Grimmauld Place, lest the Ministry of Magic catch him and return him to Azkaban. In this sense, Harry and Sirius lead parallel lives, since Dumbledore orders Harry to spend his summers with the Dursleys. In both cases, Dumbledore is simply attempting to ensure his friends’ safety, but both Harry and Sirius resent the lack of freedom that goes along with such isolation, likening it to imprisonment. Sirius grew up at Twelve Grimmauld Place but has long since dismissed the rest of the Black family, who chose to follow Voldemort. Being trapped in that house simply reminds Sirius of his alienation, just as Harry’s time at Privet Drive reminds him of his own lack of real family.
Although Mr. and Mrs. Weasley often act as Harry’s surrogate parents, Sirius is the closest Harry has to family, and Harry clearly treasures their relationship. Whenever Harry is in trouble or confused, he turns to Sirius for advice. Sirius, in turn, is protective of Harry, doing his best to assure his godson’s safety and well-being. As other members of the Order of the Phoenix have observed, Sirius occasionally confuses Harry with his father, James Potter, and Sirius’s relationship with Harry seems to be deepened by his mourning for James. Often, when Harry expresses reservations about one of Sirius’s suggestions, Sirius reprimands him for not being more like James, who thrived on risk-taking. In a way, Harry can get to know his own father through Sirius, and, surprisingly, the images he stumbles across in Book V are not the unequivocally positive ones he has always carried with him.