Maaga was the leader of a group of Drahvins who had crashed on an unknown planet after attacking a group of Rills.
Maaga killed one of the Drahvins to poison the others' minds against the Rills during their attack on the Rills' ship. She later crashed-landed on the unknown planet, waiting for the Rills to repair their ship so that she could capture it.
When the TARDIS arrived, she sent the Drahvins to capture the First Doctor, Vicki and Steven and tried to force the Doctor to help her and her crew escape the doomed planet. She died when the planet disintegrated.