Sythran was a member of the Adeptus Custodes during the Great Crusade and Horus Heresy.[1a]
Sythran was one of the Custodes under Aquillon tasked with watching over the Word Bearers before the Heresy, taking an oath of silence until his task was completed and he set foot on Terra once more.[1b] He kept his promise until shortly before his end, declaring his hatred for the Renegade Chaplain Xaphen shortly before being killed by the Gal Vorbak on Isstvan V.[1c]