An Animagus is a wizard or witch in the Harry Potter series who can transform into a specific animal at will. This ability requires extensive training and registration with the Ministry of Magic to ensure safety and accountability. Each Animagus has a unique animal form that reflects their personality or traits. The transformation process is complex and can take years to master. While in animal form, the Animagus retains their human consciousness but may exhibit animal instincts. Famous Animagi in the series include Sirius Black, who transforms into a dog, and James Potter, who becomes a stag.