Za was the son of the old woman and Gor, the firemaker of the Tribe of Gum. (PROSE: Doctor Who and an Unearthly Child) Gor taught him how to make weapons and how to make traps for bears and tigers. Za's mate was Hur.
Gor was killed in a hunt before he could pass on the secret of how to make fire to Za. Although Za inherited his father's mantle of leader of the tribe, his leadership was contested due to his inability to make fire. The issue was exacerbated by Kal, an outsider that the tribe had taken in who wished to take over. (TV: An Unearthly Child)
The secret of fire
After Kal captured the First Doctor, who he claimed could make fire, Za had the Doctor, Susan Foreman, Ian Chesterton and Barbara Wright imprisoned in the Cave of Skulls with the aim of learning the secret from them before Kal could, ensuring that he would stay in power. Upon their escape, Za and Hur pursued them.
In the forest, Za was attacked by an animal and had his wounds tended to by the strangers, who returned him to the tribe. Kal accused him of killing the old woman, but the Doctor proved that Kal had been the murderer, prompting the tribe to drive him out. Despite this, Za had the strangers imprisoned once more and, even after learning the secret of fire from them, he refused to release them.
Kal returned for revenge and Za fought him, killing him. The strangers escaped a second time, after which Za led the tribe in pursuit of them. He saw them enter the TARDIS, which dematerialised before them. (TV: An Unearthly Child)
Immortality and death
Not long after the disappearance of the Doctor, Susan, Ian and Barbara, Za and the tribe were approached by the Prometheans. They gave the tribe the "burning stone", a psychic metal which they fashioned weapons out of, allowing them to conquer various other tribes, and their armour allowed them to withstand faster-than-light travel, slowing their ageing. They went in search of more of the "burning stone" and for Ian and Barbara.
By 2013, the tribe were used by the Prometheans in their bid to rule humanity. The intellect of humans was reduced to primal levels and Za had become "leader of the many tribes", acting as the Prometheans' emissary. He and the tribe attacked the Eleventh Doctor after he foiled the Prometheans' plan, but was convinced by Ian and Barbara that there was more to humans than desire and revenge, namely his love for Hur. Za and the tribe instead attacked the Prometheans in a battle which killed both sides, with Za being one of the last to die. (COMIC: Hunters of the Burning Stone)
Upon becoming leader of the Tribe of Gum, Za was desperate to retain power and spent his time sitting and trying to make fire rather than getting meat for the tribe as Kal did, saying that it was more important that they had fire. He told his mother that she should have died with his father and threw her to the ground when she helped the strangers escape.
Za showed more respect to his mate, Hur. He listened to her advice (TV: An Unearthly Child) and it was his love for her that turned him against the Prometheans. (COMIC: Hunters of the Burning Stone) Ian helped him realise that the tribe was stronger as one when they chased away Kal. (TV: An Unearthly Child)