is a hero
He was introduced in Armageddon's Blade, and appears also in Shadow of Death. Gelu is typically only available in the campaigns, unless the map-maker has enabled him in custom scenarios.
Gelu's special ability is formidable. Even so powerful that he is typically disabled in custom made maps. While you should have no reasonable difficulty using Gelu as a main hero during the single player campaign, he could also be used as a sharpshooter-upgrading-support-hero sitting in a town garrison or following your main hero.
Dracon the Wizard