Zayl is a guardian of the balance of Sanctuary, also known as a necromancer. He first appears in Richard Knaak's novel The Kingdom of Shadow as a secondary character and later on in Moon of the Spider as the protagonist. He carries the talking skull of Humbart Wessel, a veteran fighter from Westmarch. He also carries a ivory dagger bound to his soul much like the one Mendeln wields in The Sin War.
In Moon of the Spider we become much more in touch with exactly who Zayl really is. He seems to have much more empathy than the average necromancer, a seemingly rare quality amongst their ranks.