Xerxes was considered a lunatic by his teamates, as he made constant threats to kill them in horrible ways and claimed to be from prehistoric times. During the teams mission to Salazar VII, an explosion was caused, which killed all of Xerxes teamates. He survived, but was infected by a Facehugger and later on the Chestburster tore it's way out. By some sort of miracle Xerxes survived the process, but he belived he was in the care of George Washington and Abraham Lincoln.
Tossed into a pit of dead bodies by the Aliens, Xerxes was later recovered by the new Strikeforce consisting of Sierra Cruz. Rescued and aboard Striketeam 2's ship, the doctor informed the team that Xerxes couldn't have been injured by a chestburster as he had almost fully recovered from the wounds. Unable to explain it, they would all just have to accept that Xerxes would always "remain something of an enigma".