A giant in both physical and mental terms whilst still an inhabitant of the Materium, the copper-skinned Magnus possessed tremendous innate psychic ability, and constantly sought to understand the nature of the Warp, becoming a sorcerer of formidable power.
Magnus thought he would be able to control the "Great Ocean" of psychic energy that was the Warp; however, his prodigious and careless application of his psychic gifts eventually caused him to fall out of favour with his father, the Emperor of Mankind, as well as with the majority of his brother primarchs. His psychic immaturity, recklessness, selfish pride and arrogance also caused his own undoing, as it eventually brought about his own damnation and eternal servitude to the Dark God of Change, Tzeentch.