Old Mother, better known as the old woman, was a member of the Tribe of Gum.
The old woman was the mate of Gor and mother of Za. (PROSE: Doctor Who and an Unearthly Child) She claimed to have never seen Gor make fire and was of the belief that the tribe should live without it, saying that fire would kill them all in the end. When Gor died, she believed that his death was divine punishment and she feared her son's quest to reclaim the secret. (TV: An Unearthly Child)
The strangers and death
The outsider Kal brought the First Doctor, whom he claimed he had seen making fire, to the tribe. The old woman knew her son would try to wrest the secret from this stranger and his young companions, provoking the wrath of Orb. After Za ordered the strangers imprisoned in the Cave of Skulls, the old woman waited until the tribe slept and sneaked away to the cave. She took a stone knife with her. She crawled through a secret entrance into the cave, cut the strangers' bonds and told them to flee into the forest.
Za was furious with her for having set them free, but he had no time to deal with her. Za shoved her to the ground and knocked her unconscious, then left with his mate, Hur, to pursue the strangers. When the old woman awoke, she found herself facing Kal, who was even angrier at what she had done. Kal had hoped to wrest the secret of fire from the strangers and use it to usurp Za's position as leader. The old woman had cheated him of that opportunity. He killed the old woman with a stone. (TV: An Unearthly Child)
Behind the scenes
Though her actions were mainly done out of fear rather than friendship, Old Mother may be considered to be the first ally to the Doctor and their companions.
Tragically, she was also the first character to die in Doctor Who.