Gilleah is considered the Father of Hexing. It may be that he is the Father of hexing in its current form, however we know that the original hexes were created by sorcerers on the brink of madness because of contact with Manus and by Manus himself. It is said that Gilleah never took an apprentice, so how his spells were passed down is unclear. The ubiquitous nature of the Dark Soul in humanity may be the reason that so many of Gilleah’s hexes are in use today. From the description of the Dark Orb hex we know that Gilleah was familiar with sorcery and modified old sorceries to create the Dark Orb (most likely the Soul Arrow) and Dark Hail hexes. Two other hexes are attributed to Gilleah; Twisted Barricade and Repel. These hexes both focus on defense of the caster and seem to be original spells.
We also know that hexing is viewed as a perilous affront to all life and is banned in most lands. It is likely then that Gilleah was infamous in his time and while exploring the power of hexes, became the target of persecution. This would explain the development of the defensive hexes that he is attributed with.
Gilleah’s eventual fate is unknown, but as a pioneer it may be that his was similar to the reported fate of Navlaan.