O'Brien was the captain of the HMS Alexander, which was inside a quartzberg. He rescued Nyssa, the Fifth Doctor and Kate Sherrin from a sea of crystals. He initially served Mulkris and then Eldrad. (AUDIO: Eldrad Must Die!) Retrieved from "https://tardis.fandom.com/wiki/O%27Brien_(Eldrad_Must_Die!)?oldid=2662874" Categories: Human soldiers + cat Cancel Save Community content is available under CC-BY-SA unless otherwise noted.