Gandarotethetledrax (Gandar for short) and his partner Cavis were Gallifreyan Celestial Intervention Agency agents recruited from Patrexes College. They were totally loyal to Lady President Romana III. Gandar was also a fan of the Master, prompting him to model his appearance after the infamous renegade with the goal of being the one to take on and kill the Doctor.
During a confrontation with the Eighth Doctor in Avalon, Gandar was stabbed in the heart by Margwyn but regenerated after Margwyn was unable to impale his second heart. He regenerated again shortly after this when he was impaled on a sword, with his new incarnation resembling a hybrid of human and Silurian. His new self, far more peaceful than his previous violent selves, grieved over Cavis's death.
Gandar remains in Avalon as a prisoner of war and patient of Lieutennant Anthony Cronin. (PROSE: The Shadows of Avalon)