A is for Animagus
"Please, sir. An Animagus is a wizard who elects to turn into an animal. A werewolf has no choice in the matter."
- Hermione Granger
An animagus is a witch or wizard that can transform themselves into an animal. The animal reflects the witch/ wizards personality and traits, this most certainly explains wormtail. A massive signifier for us when reading! This is a taught spell and a witch/ wizard must report that they are an animagus to the Ministry of Magic as part of the wizarding law. The spell is taught in the third year of study, we all remember the cup with a tail right?
Some animagus in HP: Professor McGonagall, Sirius Black, Peter Pettigrew, James Potter, Rita Skeeter.
Read more about animagus here.