Anzor

Anzor was a Time Lord who attended the Academy at the same time as the Doctor.

Biography
Anzor bullied the Doctor at the Academy. Years later he encountered the Doctor's sixth incarnation, who was still traumatised by his experiences with Anzor at the Academy, and forced him into a locked orbit above the planet Magnus. However the Doctor betrayed his old classmate by causing Anzor's TARDIS to fly back to the big bang slowly, knowing his foe did not have the knowledge to reverse it. (BFA: Mission to Magnus)

One account claims that the Doctor killed a bully who was tormenting him and the Master. It is possible that this bully was Anzor, and the Doctor's actions may have caused Anzor to regenerate. (BFA: Master)

Other information
His TARDIS was a type 60 and one form it took was an oak tree.