Uriel Ventris became Captain of the Fourth Company of the Ultramarines Chapter, once one of the twenty original Space Marine Legions of the First Founding, when its former captain, Idaeus, sacrificed himself during the Battle of Thracia, in a desperate last-ditch attempt to stop a Night Lords Chaos Space Marine offensive. Despite his initial disquiet at Idaeus' unorthodox methods, Ventris saw merit in them, and in time would become just as unconventional as his mentor.