Walker was a powerful supervillain from Marvel comics and a notable enemy the abstract entity, Death, of whom he had originally been attracted to in a similar manner as Thanos.
Walker was depicted as an alien death-god who decided to give Death an offering of an entire galaxy as a show of his "affection", however despite Death's infamous manipulative streaks it was not a sadistic entity and thus was repulsed by Walker's senseless destruction of trillions of lives.
This would anger Walker, taking Death's rejection as a sign of deep betrayal he devoted himself to destroying and usurping Death itself.
Walker would ultimately fail to accomplish this feat and would be destroyed by Death after several battles, fittingly it was Walker's continual sadism that proved his downfall as his cruelty towards others pushed Death into action.