The Henchman guards the Witch's Hut inside the Witch's Swamp. Players will encounter him after travelling to the swamp, but cannot pass around him.
Discovering how to get past the Henchman is the objective of the quest Goblin Problem. A lost book at the library reveals that Goblins love Void Mayonnaise, so after giving him a gift of Void Mayonnaise he'll move aside allowing the player to pass and enter the Witch's Hut.