In Battlestar Galactica, Gaius Baltar was used by a Cylon spy to help bring about the holocaust that killed most of humanity. He was rescued from Caprica, and ended up on Galactica. He invented a Cylon detector, and led a monotheistic cult. He was also elected President of the twelve colonies.
In Frank Herbert's Dune, Gaius Helen Mohaim was a Bene Gesserit Reverend Mother. She was part of the conspiracy to end Paul Atreides' rule, and was later executed by Alia Antreides.
In Jim Butcher's Codex Alera series, House Gaius is a ruling house of Alera.
In Final Fantasy XIV: A Realm Reborn, Gaius van Baelsar was a general who lead the invasion into Eorzea. He was known as The Black Wolf.
Gaius is a Latin name from ancient Rome, and means 'Happy'. Only 15 boys in the United States were named Gaius in 2015.