Thoros was present amongst the Blood Angels contingent during the Council of Nikaea. Thoros was introduced to Magnus, Primarch of the Thousand Sons by Sanguinius. He was described as one of the Blood Angels' most vaunted captains of battle.
During the introduction, Ahzek Ahriman saw a prescient flash of Thoros' death at the hands of a Megarachnid creature during the campaign on Murder. When the Emperor's Children descended to the planet Murder answering a clarion call of the Blood Angels, Thoros's helmet was found by Saul Tarvitz and presented as a gift of honour to Sanguinius (who arrived later).