Slyst was one of the High Lords which opposed Chancellor of the Imperial Council Lev Tieron's attempt to push through a Dissolution act that would free the Adeptus Custodes from their vows on Terra. He was known as a conservative reactionary resistant to any reform, and as a result was removed by Roboute Guilliman during his reforms. He was replaced by the more reform-minded Eos Ritira.
- 1: Watchers of the Throne: The Emperor's Legion (Novel), Tieron Chapter 2
- 2: Watchers of the Throne: The Regent's Shadow (Novel), Chapter 4