Carl was a robot aboard the station that housed the Zara Seven Colonial Army during the Human-Earth reptile war.
After the Silurian Qurra killed everyone on board and her people were destroyed, she lost her mind and thought she was the singer, Jen Yates, assigned to the station. She blinded Carl so that he wouldn't recognise that she wasn't human. He was her only companion aboard the station.
When the Seventh Doctor, Bernice Summerfield and Ace arrived on the station, the Doctor repaired Carl's eyesight. Now recognising "Jen" as the enemy, Carl attacked her. Ace was forced to destroy Carl so that he wouldn't kill Qurra. (PROSE: Cold War)