Gar'tok

From The Stargate Omnipedia

Jaffa master in service to Apophis. Gar'tok supervised the instruction of several humans trained to one day infiltrate the Tau'ri. He showed Captains Rogers and Nelson a cave where weapons -- real weapons, not training intars -- would be used for the final challenge and eventually Earth's defeat.

Gar'tok then left the trainees to aid Apophis in a great battle, and was likely killed.

KEY EPISODE

Rules of Engagement - Rogers tells of Gar'tok involvement in the training prior to his abandoning the team.