King Stevenson was a monarch who controlled the land that the Forest was part of and he had traveled to the Forest in order to meet the Forest God, as well as to try and find the Huncher and her hollow. It is unknown why Stevenson either wanted to meet the God or the dreaded Huncher, but some of his dialogue suggest that it was linked to how his relation, Baroness Lalopsey, had previously owned the land that the forest resided in and had suddenly died, her ghost now haunting her former manor. It could be that Stevenson felt that either the God or the Huncher was responsible for this.
With him, Stevenson had his entourage, which consisted of his adviser (a ginger cat), an armored bodyguard, and a musician. Stevenson was planning to use the arm of a severed criminal ("Donated, of course!") to light the way to the Huncher's Hollow. However, after Adina meets the Forest God, she finds the severed head of Stevenson's bodyguard, meaning something attacked them. Whether it was possibly the Forest God, the Huncher, or even the Kid, is unknown, and the fate of Stevenson himself is a mystery.
Strangely enough, Stevenson bears an eerie resemblance to Mae in physical appearance, whether this is symbolic or another foreshadowing is also unknown. The Advisor also bears some resemblance to descriptions of Casey Hartley, so this could mean Mae's grandfather based these two character's looks off of Mae and her friends.