Tigellans were a race of humanoids. They were native to Tigella.
Tigellan society was split between two groups: the Deons and the Savants. The Savants were the logical scientists of the Tigellans who ran the planet and wanted to study the Dodecahedron. The Dions were the religious Tigellans who worshiped Ti and believed the Dodecahedron to be a holy object. (Meglos)
The Tigellans lived underneath the surface of Tigella due to the dangerous plant life on the planet. Meglos, a Zolfa-Thuran, disguised himself as the Fourth Doctor and stole the Dodecahedron. Lexa, leader of the Deons, did not believe the real Doctor’s tale of someone using his appearance. The Deons staged a revolution in anger At The Doctor’s admission into the power room. A Gaztak party attacked the Tigellan city and took Meglos and the Dodecahedron back to Zolfa-Thura. (Meglos)