Heracleon is a Tribune within the the Adeptus Custodes and commanded the Hetaeron Guard during the fifth year of the Thirteenth Black Crusade. It was also during that year that the name of Shield-Captain Valerian came to him in a dream and great importance was given to this, as Custodes are rarely capable of dreaming. In fact, Heracleon was the first Custodes in a millennia to do so and he felt that this signified that Valerian was a candidate to join the depleted ranks of the Hetaeron Guard. Shockingly, however, Valerian failed in the first trial to join the Guard, as he was physically unable to make himself enter the chamber of the Golden Throne which held the Emperor's ravaged body.
- 1: Watchers of the Throne: The Emperor's Legion (Novel), Valerian Chapter 2