Ganatus was a member of the Thal expedition which Temmosus led to the Dalek city in search of food. In contrast to Temmosus and Alydon, Ganatus doubted that the Daleks would be willing to help his people. Noting how his people had once been fierce warriors and were now peaceful farmers, he wondered aloud if the race they had once known as philosophers, teachers, and scientists might now be the bloodthirsty killers. His suspicions were more than justified when the Daleks ambushed the Thals after inviting them into the city with a promise of food, killing Temmosus.
After the Doctor and Ian convinced the Thals of the need to fight for their survival, Ganatus was among those who agreed to accompany Ian and Barbara on their expedition to seek another way into the city via the Daleks's water supply system. During this experience, Ganatus was impressed by Barbara's tenacity and courage, and even became enamored of her. He was also among the few Thals to survive the expedition and join in the final battle which defeated the Daleks, for the time being.
Ganatus was present to bid the Doctor and his companions farewell, giving Barbara some cloth to make a dress. Ganatus expressed his wish that she could model the finished dress for him, a not too subtle hint that he wished her to stay. Barbara was herself relunctant to leave Skaro, but still departed in the TARDIS, leaving Ganatus to work with his people in rebuilding their world ("The Daleks"). Barbara however never forgot him, and one of the names she and Ian later conferred on their son, John was Ganatus ("Byzantium!").