Brother Mascios was Space Marine in the Scythes of the Emperor Chapter, shortly before the fall of Sotha. He was a member of Sergeant Hekaton's Tactical squad, and bore his name upon his pauldron.
Mascios was part of the crusade to liberate the reliquary world of Egottha in 990.M41, travelling aboard the Xenophon.
When the ship was attacked by Tyranid forces, Mascios was assigned to accompany Serf-sergeant Milus Ogden and his fellow security officers in the procurement of weaponry and equipment from the ship's stores. He saved Ogden's life when the vessel was struck by debris, and later formed an almost paternal bond with the serf.
Later, after almost single-handedly destroying a Tyranid Ramsmiter, Mascios was killed while attempting to repel a xenos boarding party.