Theiss is a Tanith senior officer in the Tanith First Regiment. He is first mentioned in Honour Guard, as a Sergeant, where he fights at the Shrinehold. On Aexe Cardinal, his platoon, like Obel's, in bombarded by Shadik shellfire, and takes casualties. He is mentioned as being usually cheerful. He is not mentioned in great detail up until The Armour Of Contempt, where he had been promoted to Captain and becomes the commander of M Company. He leads his company in combat at Hinzerhaus, which he survives. He is mentioned again in Blood Pact, during the senior officer's meeting.