Katarina is a replacement for Vicki who exited the cast in "The Myth Makers", the same story that Katarina entered it. The story takes place in ancient Greece during the Trojan War. Vicki falls for a Trojan soldier and decides to stay behind when the TARDIS leaves. Katarina is scooped up by the doctor and taken into the TARDIS for safety during the height of the war.
Katarina was only a Dr Who companion for 6 episodes. She exited by opening an airlock and killing herself and a bad guy who was threatening the TARDIS crew. She thereby became the first companion to be killed during an episode.
Katarina is played by Adrienne Hill. She was born on July 22, 1937 and died on Oct 6, 1997.