Za was the leader of a primitive tribe circa 100,000 BC. To preserve their power and authority, the tribal leaders kept a monopoly on the secret of making fire. The secret and leadership was passed down from father to son. Unfortunately, Za’s father was killed during a hunt before he could pass on the secret. Unable to make fire for his people, Za found his leadership in jeopardy, more so with Kal, an outsider taken in by the tribe, hoping to take over.
Za’s fears seemed confirmed once Kal had captured the First Doctor, claiming that he had seen the old man make fire. Za ordered the stranger and his three companions imprisoned in the Cave of Skulls, hoping to wrest the secret of fire from them before Kal could and so stay in power. The strangers escaped, Za pursuing them together with his mate Hur.
Za was attacked by a forest animal. The Doctor and his friends tended to his wounds and took him back to the tribe.
Despite this, Za still had the strangers reimprisoned. Even after they taught him the secret of fire and helped him defeat The would-be usurper Kal, Za still refused to release them.
Shortly afterward, Za and the tribe were approached by the Prometheans, who gave them the “burning stone” (Psychic metal), which imbued them with power and immortality.
In the present, the Promethean used their tribe in their bid to rule humanity, reduced the modern-day humans’ intellect to primal levels, and having Za become “leader of the many tribes”, acting as the Prometheans’ emissary.
The Eleventh Doctor foiled the Promethean’s plan, and Za and the tribe attacked him. Ian Chesterton and Barbara Wright managed to convince Za that there was more to humans then desire and revenge, like love. Za, realising he loved Hur (and vice-versa) stopped his attack on the Doctor. The Prometheans attacked Ian and Barbara, incensed by their interference. Za realised the Prometheans had lied to him, and led the tribe in attacking them. In the ensuing battle, both the Tribe of Gum and the Prometheans perished, Za being one of the last to fall. (Hunters of the Burning Stone)