He is a zombie-king created by Herobrine, and was the forerunner of Xa-Tul.
The Birth of Herobrine
Vo-Lok acts as Herobrine's second-in-command during the war, leading the army of zombies to attack the NPC villages. The NPCs, led by Smithy and Gameknight, resist every attack.
A major battle takes place at Two-Sword Pass, where Smithy is killed in battle. Gameknight, having taken upon Smithy's mantle, engages Vo-Lok and kills him.
- In Trouble In Zombie-Town, Gameknight and Crafter have a discussion about how Xa-Tul was the name of a zombie general who lived during The Great Zombie Invasion. The zombie they were referring to was most likely Vo-Lok, having been renamed by the author so that the readers wouldn't confuse Vo-Lok with Xa-Tul.
- Whereas Two-Sword Pass is called that name by the NPCs, the monsters call it Vo-Lok's pass in honor of the fallen zombie king.
Minecraft: Story Mode (2015)