Thirteenth Drax

Drax was a renegade Time Lord with a knack for tinkering. He had known the Doctor before either left their home planet of Gallifrey.

Youth
Drax attended school on their home planet Gallifrey with the First Doctor. (DW: The Armageddon Factor)

As a youth on Gallifrey, Drax had a skimmer he had built himself. Both Drax and the Doctor belonged to the Deca, a social group of rebellious students at Prydon Academy. Drax and Mortimus became the first two members of the Deca to permanently flee Gallifrey and turn renegade. (PDA: Divided Loyalties)

As a Renegade
Drax did jail time in Brixton on Earth, where some of the local accent rubbed off. With the Fourth Doctor's search for the sixth and 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 Third planet, ruled by The Shadow.

The Shadow had imprisoned Drax and made him work for him. He agreed to help the Doctor. With his assistance, The Doctor recovered the final segment of the Key to Time. Afterwards, Drax stayed on Atrios to offer his services to help rebuild. (DW: The Armageddon Factor)

Behind the scenes

 * The exchange between the Doctor and Drax regarding his accent in The Armageddon Factor would be echoed decades later in a similar exchange between Rose Tyler and the Ninth Doctor in Rose.


 * The Make Your Own Adventure with Doctor Who book Search for the Doctor included Drax as a character that the reader/main character could interact with. He and K9 helped the reader defeat Omega and rescue the Sixth Doctor. In this book his TARDIS was in the shape of a convertible car, the number plate of which read "TARDIS."
 * A widely popular fan theory speculates that the character of Quixotl from Alien Bodies is Drax in a future incarnation.