Maggard was a mute bodyguard who was indentured to Petronella Vivar, a remembrancer from a noble house. His vocal cords were removed at some point, as Vivar was of the belief that servants should not speak in their mistress' presence. Maggard was an exceptional warrior, wielding an ancient Terran blade with incredible skill. He also had golden eyes.
Maggard relays messages to Vivar via a mnemo quill, which literally puts his thoughts on paper. however, one time, as he left, the mnemo quill wrote "...cking bitch...", showing that he did not like his service, or Vivar.
Maggard accompaned his mistress to the surface of the plagued moon of Davin, and defended her with such skill that he attracted the notice of the Warmaster Horus himself. Deeply moved to be honoured by the Warmaster, Maggard offered Horus his sword, the gesture saying what he could not: "I am yours to command."
Later - either as a reward for his service, or some part of a greater plan, he could not be sure - Horus killed Vivar, and Maggard swore his full allegiance to him. He served as chief enforcer to Maloghurst, Horus' equerry and master of intrigue, and was genetically enhanced by Horus' apothecaries to become more like the Space Marines.
During their escape from Horus' flagship, the Vengeful Spirit, Captain Iacton Qruze and the remembrancers he was leading to safety encountered Maggard in the flight deck of the ship, and Qruze became locked in combat with the silent assassin. As he was trying to stave off his end, intervention from Kyril Sindermann — who had picked up Maggard's pistol and wounded the murderer with it - gave the old veteran Qruze the opening to stab his blade through Maggard's chin and into his brain, killing him instantly.