Thirteenth Drax

Drax was a Time Lord who went to the same school as the Doctor and helped him obtain the Key to Time.

During the Doctor's search for the final segment of the Key to Time, the Doctor and Romana arrived on the planet Atrios, which was at war with their neighbouring planet Zeos. In reality, the planet Zeos was deserted save for a giant computer called Mentalis, which was controlling the war. The true enemy was a third planet called the Planet of Evil, ruled by "The Shadow".

On the Planet of Evil, the Doctor encountered Drax, an old Academy friend and a fellow Time Lord, who had been employed under duress by the Shadow, but agreed to help the Doctor. Through his assistance, The Doctor recovered the final segment of the Key to Time. (DW: The Armageddon Factor)