Sirius Black is a fictional character from the Harry Potter series created by J.K. Rowling. He is introduced as the godfather of Harry Potter and is known for his rebellious nature and loyalty to his friends. Sirius was a member of the Order of the Phoenix and was wrongfully imprisoned in Azkaban for a crime he did not commit. Sirius comes from the Black family, a lineage known for its dark wizardry. He is an animagus, able to transform into a large black dog, which symbolizes his connection to loyalty and freedom. Throughout the series, Sirius plays a crucial role in Harry's life, providing guidance and support.