Caius is a vampire, one of the three ancient leaders of the Volturi, who are based in Volterra, Italy.
Caius is described as having pale, translucent skin, and the red eyes of a human blood drinking vampire; he finds drinking animal blood as repulsive. He has shoulder length silvery-blonde hair, which is close to his skin colour.
Caius is probably known best as the cruellest one out of the Volturi, and is described as 'merciless'. He is usually in favour of executions, and old-fashioned methods of punishment. In Breaking Dawn, Caius was out-voted in the decision on kiling Renesmee. However, Caius found a way to shed blood in Irina. He pressed charges against her for false accusations and had her immediately murdered , in front of Irinas sisters, Kate and Tanya, in the hope that they would retaliate. He likes the sight of bloodshed, war and is very stubborn when it comes to fighting or killing.
He was born in 1200BC, and was made a vampire at some point during his middle aged years. He later joined the Volturi, along with the two other leaders, Aro and Marcus. Later two female vampires joined the Volturi: Sulpicia and Athenodora. Athenodora later became Caius's wife, and Sulpicia became Aros. 2000 years before Breaking Dawn, he was nearly killed in a fight with a werewolf, which prompted him to get them hunted to near extinction. He also took part in the extermination of the Immortal Children.
Jamie Campbell-Bower was cast in the role of Caius. It is unknown if he will reprise his character in Breaking Dawn.