Ordo Mallaeus Grey Knight Leader is an unnamed Grey Knight seen accompanying the trio of Inquisitors.
TTS Canon Edit
The Grey Knight Leader helped to round up suspects during the Inquisition's purge of Terra. Later, he was eager to discover Kaldor Draigo in the warp, seeing him as their best chance at survival. 
- It's unclear if the character is part of the Grey Knights proper or the Ordo Mallaeus; while the two organizations work together, the Grey Knights nominally aren't inquisitors themselves.
- Leman Russ claims that the Grey Knight Leader's accent is "strange and full of waffles." This is likely meant to be a jab at Eliphas, who is Belgian.