Belgaroth

Belgaroth the Lord of Fright is a higly powerful undead Chaos Knight who serves as the main villain and final enemy in the Fighting Fantasy gamebook Knights of Doom. He was once a holy templar and the brother of Chivalras IX the wise king of Ruddlestone, who renounced his alliegances and turned to the Dark Gods, becoming one the most powerful and the most feared Chaos Lord ever seen on the world of Titan. Belgaroth can compete with Razaak for the title of the best protected and hardest to defeat Fighting Fantasy villain ever seen. Knights of Doom itself being widely regarded by fans as one of the hardest gamebooks of the entire series.

Trivia

 * Belgaroth and Razaak are very similar Fighting Fantasy final bosses: both are undoubtedly the hardest ever seen, both needs an insane amount of knowledge and special spells of item to be faced safely, (with an item that can kill the player) and both are formidable foes with special rules that makes them nearly undefeatable. Belgaroth is less hard in one-on-one battle, though. But in turn, the player must win many VERY TOUGH battles and needs the aforementioned knowledge and items before AND AFTER fighting him.
 * Belgaroth is also similar to two other Fighting Fantasy villains: Voivod the Waster and Mortis of Balthor, who are also powerful Dark Knights and Evils from the past, who need a magical spear to be defeated. This similarities with Voivod are stronger, as both are demonic Chaos Lords who control a formidable team of Dark Knights.
 * Oddly enough, Belgaroth shares his name with a planet of the Star Wars extended universe.
 * Belgaroth's page on Titannica, the Fighting Fantasy Wiki: http://fightingfantasy.wikia.com/wiki/Belgaroth