The hulking Mammoth was first seen as a member of the Shi'ar Imperial Guard when Lilandra journeyed to Earth to take the X-Men's mentor Professor X on a diplomatic mission to the Shi'ar homeworld. However, Xavier's genetic twin Cassandra Nova had switched bodies with her brother, and once onboard the Shi'ar Superdestroyer she attacked the Imperial Guard. Mammoth was amongst the first Guardsmen to fall under Nova's onslaught.