The plot follows BioWare's own canon, meaning it may not follow some of the player's choices in the games.
This section contains spoilers for: Dragon Age: Knight Errant.
Gaius served as Magister Qintara's valet for years. Upon the magister's death, Gaius impersonated him, using pyrotechnics to keep the illusion that he was still alive and experimenting within his estate. Gaius' true master is Fen'Harel, for whom he gathers information on the human world. After he obtained a weapon imbued with Red lyrium stolen from Kirkwall, he traded it away for information to House Danarius. According to writer Nunzio DeFilippis, this was not something Solas would have approved of.
Gaius is slain by invading Qunari while trying to flee the Qintara estate.