Fulgrim(Demon Prince)

Biography
One of the twenty Primarchs created by the Emperor of Mankind to lead the armies of the Imperium's Space Marines.
Kidnapped as a baby by the four Chaos Gods and scattered across the galaxy, he landed on the isolated mining planet Chemos, where he was found and adopted by a police officer.
Reunited with his father when the Emperor arrived on Chemos, Fulgrim swore allegiance to his father and was given command of the Emperor's Children, a Space Marine legion created from Fulgrim's genetic template.
He was corrupted by Slaanesh's influence after defeating the serpentine species of Slaaneshi (the Laer) on their homeworld of Laeran. This corruption was further exacerbated by Fulgrim's possession of the "Blade of the Laer," a weapon possessed by daemons.

Capabilities
Primarch Physiology: Superhuman strength, speed, endurance and heightened senses.
Longevity and Immunity: As a Primarch, he is virtually ageless, resistant to disease, and able to survive in conditions that would be lethal to mortals.
Enhanced Healing: His regenerative physiology allows him to quickly recover from severe wounds.
Corruption of Slaanesh: After his fall, Fulgrim's powers were augmented by the Chaos God Slaanesh, granting him heightened reflexes, supernatural perception, and supernatural resilience.

Equipment
The Daemon Blade Laer was a cursed weapon that enhanced Fulgrim's skill and accelerated his corruption.
The Fireblade is a golden-bladed power sword forged by Ferrus Manus, Primarch of the Iron Hands. It constantly emits the same powerful flames in which it was created.

Role in the plot
Fulgrim willingly accepted the patronage of Slaanesh, the Dark Prince, who found a trustworthy servant in the primarch, whispering enticing words of great perfection to him.
By the time Horus laid siege to Terra, Fulgrim had reached daemonic apotheosis and was no longer in control of himself. This was reflected in the Emperor's Children: the Primarch did not strengthen the Legion, but, on the contrary, distanced himself from it.