Once a proud member of the mighty First Legion, Moritat-Prime Erusar was among the five hundred space marines that, alongside Luther the Arch-Betrayer, were sent back to Caliban during the Great Crusade. Despite his pleas to go with his gene-father and undertake suicidal missions that others were unwilling to complete, Erusar's superiors declared that the Lion had no use for "paltry assassins". Stricken with grief and with his head hung low, Erusar joined his brothers upon Caliban. He would go on to eagerly join them in Luther's rebellion against the Primarch, striking down a dozen of his former comrades before being sucked away into the Sea of Souls, and would not appear for another millennia.