James Potter takes the form of a stag as an Animagus in J.K. Rowling's Harry Potter books.
James learned to become an Animagus while attending Hogwarts, alongside Sirius Black and Peter Pettigrew. His stag form inspired his nickname, Prongs. The three students became Animagi illegally so they could accompany their friend Remus Lupin during his monthly transformations into a werewolf.
James's animal form also connects to Harry. Harry sees a stag associated with his father during the events surrounding the Patronus charm, although the magical form involved is a Patronus rather than an Animagus transformation. The resemblance is deliberately emotional and symbolic.
Sirius's Animagus form is a large black dog, known as Padfoot, while Peter's is a rat, known as Wormtail. Remus is not an Animagus; he is a werewolf. These distinct forms are often confused because the Marauders' nicknames and magical identities are revealed across several books.