Hasgard was, in his previous existence, an Ice berserker, known among his people as “The Warrior Who Will Not Die”, such was his capacity to sustain wounds without any diminishment of his bloodlust. Of course, he did in fact die, but not in battle. Smallpox denied him that honor by killing him on the eve of his 40th birthday.
Necronumos, well aware of Hasgard’s prowess, travelled north to seek out his grave and “recruit” him to the Undead horde. Unlike most of his Undead comrades, Hasgard has no bitterness regarding his death, and no wish to return to the peace of the grave. Having had the honor of death in battle stolen from him by disease, he relishes the opportunity to die in battle again and again in undeath.
All Undead Champions have been brought back to life at least once already, but Hasgard is unique in that he is able to resurrect himself yet again. And he comes back from death as an even more dangerous foe, capable of attacking at double speed. This makes him the absolute best Champion for shock assault “suicide missions”, so he’s a popular choice for the centre frontline.