Zastor was the leader of the Tigellans. He summoned the Fourth Doctor to Tigella when the Dodecahedron's power began failing. He hoped to mediate a truce between the Deons, led by Lexa, and the Savants, led by Deedrix.
Zastor met the Doctor during his first visit to Tigella. He summoned him to help with the power fluctuations they were experiencing. However, Meglos disguised himself as the Doctor and stole the Dodecahedron. As confused as he was, Zastor believed the real Doctor and his stories of someone stealing his appearance. Lexa, however, did not.
The Deons staged an uprising and Zastor was taken prisoner. A Gaztak attack meant that the Deons were needed and so he was let loose. He helped prevent the Doctor's sacrifice and calmed the revolution. After defeating Meglos, the Doctor returned to Tigella to bid Zastor farewell. (TV: Meglos)