Prongs
From UnknowableWiki
Prongs is the nickname of James Potter, one of the four Marauders. It is given to him during his Hogwarts days due to the fact that his Animagus form is a stag (PA22).
Sirius refers to James as "Prongs" when the two students are duelling against Snape near the Great Lake, after their OWLs (OP28).
The Marauder's Map is signed with the four Marauders' nicknames:
When the Map communicates with people who do not know the password to open it, statements by all four Marauders appear on the blank parchment; each of them is signed by one of them. Severus Snape attempts to force the Map to reveal its secrets to him after apprehending it one night; Mr. Prongs calls him an ugly git (PA14).
Fred and George Weasley, who find the Map in their first year at school, fondly refer to the its creators—whose real names they do not know—with gratitude, feeling that they owe much of their success to the Map (PA10, PA13).
After Albus Dumbledore learns that Harry Potter's Patronus is a stag, he assures Harry that James still lives inside his son. "'Prongs rode again last night," he says (PA22).
