Brother Chaplain Halrun Hal of the XVII Legion (Word Bearers)
Brother Chaplain Halrun is the de facto leader of the Word Bearer elements on Terminal 509.
As a chaplain, Halrun is responsible for maintaining his assigned unit’s spiritual well-being. To outsiders, he may appear cold and aloof, but amongst his own Battle Brothers, he is highly energetic, immensely inspirational and almost father-like in his attitude towards his flock.
Brother Chaplain Halrun led his men from Terminal 509 moments before the sabotage, attempted by two Battle Brothers from his Legion. His current whereabouts is unknown.
Update: Halrun revealed himself to the players on Cassandria after the ambush on Populonia. He used a mechanicum abomination in his employ to extract the Gene seed of three of the captive Astartes. Whatever else he had planned, it was foiled by the intervention of a civilian.
After escaping, the Astartes learned that Halrun and a small fleet had departed for terminal 509, intent on destroying the station.