Oz's best friend and loyal servant. To him, Oz is his most precious person, and he is willing to sacrifice anything for him. He was taken into the Vessalius family after being discovered in an injured state 15 years ago. He was invited by Oz to attend the coming of age ceremony as his friend. During the ceremony, he was controlled by a chain in the Baskerville's possession and forced to attack Oz. After regaining consciousness, Gilbert manages to see the face of one of the hooded people and for some reason jumps in the way of Oz's attack to protect him.

Source: My Anime List