James Potter's Animagus form was a shining red stag (Prongs), Sirius Black's was a shaggy black dog (Padfoot), and Peter Pettigrew's was a fat grey rat (Wormtail). As 'Padfoot' and 'Prongs', Sirius and James were large enough to control Remus (Moony) during his monthly transformations into a werewolf.

How did Sirius get the nickname Padfoot?

Sirius' form took the shape of a huge black dog (not unlike the Grim), from which his nickname "Padfoot" was derived. James would become a stag (Prongs) and Peter would become a rat (Wormtail). ... Although he later considered himself "an idiot" during this time, Sirius, along with James were immensely popular.

What does the name Padfoot mean?

1 dialectal, England : goblin — compare barghest, boogeyman.