As a first son of a minor noble house, Mikhail Tertren was a LCAF Hauptmann in the 12th Lyran Regulars. In 2928, an ill-fated raid against Stewart (in retaliation for an earlier, rather destructive raid on Solaris VII) led to the capture of many men and women from the 12th, including Tertren, by the Free Worlds League.
Having taken the Lyran characteristics of opportunism and business-first-ethics to heart, Tertren offered to work for the Free Worlds League. The captives from the 12th were thus released on New Year's Eve in what seemed to be a magnaminous gesture by House Marik, but in truth served to repatriate the traitor back into the LCAF. He would end up serving in the LCAF Strategy and Tactics Division.
Tertren's aid to the Free Worlds League proved very damaging to the Commonwealth. He provided vital information for a Marik raid against Shiloh and advised the League to make extensive use of terrorist squads to foster unrest on border worlds.
Lyran counterintelligence eventually narrowed the identity of the spy in their midst down to four possible candidates and in 2937 set up four separate operations, one masterminded by each suspect without knowledge of the others. As hoped, only one operation met unexpected resistance from League troops that shouldn't have been near the target, identifying Tertren as the prime suspect. However, he managed to elude capture and vanished into the periphery in 2938. All efforts to apprehend him proved fruitless.
Even after his identity had been uncovered, his actions continued to hamper the Commonwealth. The paranoia about him led to tight security protocols, which slowed LCAF operations on the border considerably and resulted in the League winning more border skirmishes than the Commonwealth in the following decade.
In 2952, the Free Worlds League attacked and took Cavanaugh II. Spearheading the assault was the Third Marik Militia who, after some sort of a training break, had markedly improved their tactical acumen against Lyran forces. House Steiner commanders thus marked the Third's commander as a priority target and sent the Eridani Light Horse's 5h Striker Battalion (of the ELH's 21st Striker Regiment) on a headhunting mission instead of recapturing the planet. The mission downed the enemy commander's Marauder and killed him. Upon inspecting the pilot, it was found that it had been none other than Mikhail Tertren.
It was noted that Tertren had been given command of the Third upon his return from the periphery in 2952, and would command the unit for five years; this in turn seems to establish the headhunting mission only killed him five years later, in 2957.
- House Steiner (The Lyran Commonwealth), p. 71 - "The Traitor Tertren"
- Handbook: House Steiner, p. 49
- House Marik (The Free Worlds League), p. 41