Astrid was a Federation officer with the rank of Colonel, and a commanding officer of the 5th Legion. After the Intergalactic War, the survivors of the Legion arrived on Sardos and took control.
He was responsible for the creation of Moloch by running the Sardoan computer projection through the energy/mass transformer to create a specimen of the creature into which the Sardoans would eventually evolve. After attempting to destroy Moloch, Astrid was later imprisoned by Moloch, and his second-in-command had "an accident", leaving Grose in command. At some point before this Astrid sent a communication to Servalan reporting his suspicions of Grose's loyalty.
It was revealed that Astrid had been kept in a tank in Moloch's computer room, in a state of sensory deprivation whilst retaining full consciousness. His life support system was still working up to and including Moloch's ill-fated teleport to the Liberator but it wasn't made known whether he survived the events. (TV: Moloch)