The Commanding General of the Holy Empire's army that defeated the Gael Tribe in Erin Island. He believes that ideals are things that allows one to fight and achieve their goal. He doesn't believe in fighting for others or in the name of friendship to which Arthur greatly opposes.He has met Arthur at a meeting 4 years ago before the starting of the anime. He later returned to crush the Gael rebellion that was happening in Albion where Londinium, the Holy Empire's trade center faces threat from the Gael Tribe.

At his first encounter with Arawn, Arawn tells him that the only thing he desires is "regius"(meaning-royalty but it can also denote "little king"). He also told him that the day he will decipher the true meaning of the word he shall face his death. Until their final battle at Avalon he thought that Arawn wanted royalty but during his battle with Arthur he realised the true meaning of "regius". He was then killed by his hands. As a dying soldier he asked for a favour to Arthur(or rather he referred to him as "little king") to spare the lives of his men even though they tried to kill the Gaels and wanted to take over Avalon. Arthur concerns with Arawn but makes his own decision to do the favour. Before dying Gaius also commands Dekimus, his subordinate to surrender to the Gaels.

He wields a great sword, and is the only member of the Holy Empire to wield it proficiently.