Sirius Black is a major character in the Harry Potter originally making his debut as the titular false main antagonist of Harry Potter and the Prisoner of Azkaban. He is an animagus with the power to turn into a black dog who was entrusted with the task of protecting Lily and James Potter from Voldemort and the Potter's made him the official godfather for their son Harry for his loyalty however he was then framed for turning them over to Voldemort and sentenced to life in Azkaban. However after 12 years he managed to escape and reunite with Harry and aide him on his quest to stop Voldemort and even told him who the real culprit was.