"Gerry" was a Chameleon who had taken over the identity of Gerry of the leisure world Krennos. He was romantically involved with another Chameleon, "Susie".
When the Sixth Doctor, Crystal, Jason and Zog landed on Krennos, the Manager wondered if this Doctor was the same as the one they had met before. He ordered Gerry and Susie to have the Doctor's companions killed, then changed his mind because it might make the Doctor suspicious, then changed it again when Zog found the swimming pool containing the bodies of those used by the Chameleons.
When the plant life began attacking the dome, there was nothing that could be done to stop it. The Manager absorbed the planet's identity and put it in a coma. He was killed in the process. Gerry and the other Chameleons had to be "deprocessed" and leave Krennos. (PROSE: Face Value)