Fourth Drax

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

Youth
Drax attended Prydon Academy with the the the Doctor in the Class of 92. They were on the tech course together. Though his practical work was satisfactory, he failed his exams, done in by Temporal Theory. (DW: The Armageddon Factor) Drax and the Doctor belonged to the Deca, a social group of rebellious students at Prydon Academy. Drax and the Monk became the first two members of the Deca to permanently flee Gallifrey and turn renegade. (PDA: Divided Loyalties)

As a Renegade
Upon going renegade, Drax travelled the universe doing repair and maintenance work in the fields of cybernetics, guidance systems, and armaments. When Drax's TARDIS suffered a breakdown in its hyperbolics, Drax was caught on Earth engaging in criminal activity to procure replacement parts and did time in Brixton prison]].

Later, the Black Guardian's agent The Shadow, imprisoned Drax and forced him to build and maintain a giant computer called Mentalis on the deserted planet Zeos. Mentalis carried out a war against the neighbouring planet of Atrios.

Four hundred and fifty years later in their personal timelines, they met again. While searching for the last segment of the Key to Time, the Doctor and Romana arrived on Zeos. Drax, under The Shadow's orders, reluctantly lead the Doctor into a trap. Easily seeing through Drax's pretence, the Doctor talked him into joining forces against the Shadow. With Drax's assistance, the Doctor recovered the final segment of the Key to Time. Afterward, Drax stayed on Atrios to help rebuild that world. (DW: The Armageddon Factor)

Personality
Drax showed extreme technological aptitude. As a youth on Gallifrey, Drax had a skimmer he had built himself. (PDA: Divided Loyalties) However, Drax found himself unable to grasp temporal theory, and he failed the class. (DW: The Armageddon Factor)

During his prison stay Drax picked up Brixton's local accent and idioms, which remained part of his speech patterns after he left Earth and resumed his travels. When Drax met K9 Mark II and marvelled at the "little tin dog," K9 made note of Drax's silliness. Although Drax was not above criminal activity and weapons dealing for personal gain, he displayed a sense of what was morally right and bemoaned having to assist the Shadow in his schemes. The Doctor was able to talk him round to joining him against the Shadow without much trouble. (DW: The Armageddon Factor)

Behind the scenes

 * Drax was Barry Jackson's third guest role in Doctor Who, after Ascaris and Jeff Garvey.


 * 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 interactive Make Your Own Adventure with Doctor Who book Search for the Doctor included Drax as a character. In this book Drax's TARDIS was in the shape of a convertible car, the registration plate of which read "TARDIS."