Remus and Sirius

Sirius and Remus met at Hogwarts in their first year. They, along with James Potter and Peter Pettigrew, became close friends, collectively known as the Marauders. They were known to have a passion for mischief and were generally well-liked by their teachers and peers.

In their second year, Sirius, James and Peter discovered that Remus was a werewolf. At some point, James, Sirius and Peter decided to become Animagi (a wizard who can transform into an animal at will), as this would make werewolf transformations more bearable for Remus. By their fifth year, they completed the Animagus transformation: Sirius was able to become a shaggy black dog known as Padfoot, James was able to become a stag and Peter was able to become a rat. Every full moon, they all would sneak out and meet up with Remus in the Shrieking Shack.

After they graduated from Hogwarts, they joined the Order of the Phoenix together. However, when they became aware that there was a spy in the Order, Remus suspected Sirius and Sirius suspected Remus. This led to Sirius not telling Remus that he had switched places with Peter as the Secret Keeper for the location of their friend James and his wife Lily. As such, when the Potters were betrayed, Remus (along with the rest of the country) believed Sirius was guilty. At the time of Lily and James' death, Remus was in the north of the country on Order of the Phoenix business when he discovered what had apparently happened. Sirius was imprisoned in Azkaban for supposedly murdering Peter and twelve Muggles with one curse.

They were separated for twelve years during Sirius' imprisonment in Azkaban. In 1993, Remus discovered that Sirius was innocent when he spotted the supposedly-dead Peter Pettigrew on the Marauder's Map, and was reunited with his old friend. They both apologised for doubting each other, but had to separate again as Sirius went on the run from authorities. When Voldemort returned in human form, they both rejoined the newly reformed Order and fought against Death Eaters together, including at the Battle of the Department of Mysteries,