What was Sirius Black's nickname in the Marauders?

The story behind the answer

Padfoot was Sirius Black’s nickname among the Marauders because his Animagus form is a large black dog—dogs move on padded feet, hence “Padfoot.” Alongside James Potter (Prongs), Remus Lupin (Moony), and Peter Pettigrew (Wormtail), Sirius used this form at Hogwarts to roam safely and support Remus during full moons.

Fun context and memory tip: the Marauders also created the Marauder’s Map. Think “pads on a dog’s feet” to recall Padfoot, and remember that Sirius is named after the Dog Star, making a dog-themed nickname perfect. “Padfoot” also echoes British folklore of a ghostly black dog, neatly matching Sirius’s stealthy canine form.