Peter Pettigrew also known as Wormtail is one of the biggest traitors in fiction.
He grew up in Hogwarts as best friends with Remus Lupin, Sirius Black, and James Potter.
He even joins the Order of the Phoenix, and defects to Death Eaters after Voldemort tries to kill him. He tells Voldemort the location of the Potters, and frames Sirius Black for murder.
He later becomes a rat for years.
But gets found out.
He escapes, kills Cedric Diggory, and revives the Dark Lord.
He is rewarded by being nothing but a servant to Severus Snape, and other Death Eaters. Then he chokes himself. Thank god.