Boon> is an expanded universe character who appears only within the Hollow Knight Comic's First Chapter: Quirrel (despite being called a first chapter no other comics have been released since). They are first encountered by Quirrel, being attacked by a horde of vicious bugs in the plains outside of any kingdom. Quirrel quickly intervenes and Boon is rescued from the attackers. After which Boon shares a meal with Quirrel out of gratitude. While Quirrel's goal in the comic is to reach Hallownest, Boon splits paths with Quirrel before reaching the kingdom and their eventual destination is unknown.
Earlier in the comic Quirrel makes a note about the wilderness beyond any kingdom:
"Out here, only the simplest adapt, those who bear no burden of mind, only the drive for survival. Perhaps thought is our weakness?"
This line connects to the immediate encounter with Boon, as they are shown with a "burden of mind" and thus shown to be overpowered by the more primal creatures. Though sapient and able communicate through words, Boon strangely talks in a very broken up and simple manner; leaving it open to how developed their mind is and how they developed it to begin with. As even Quirrel seems unsure of the mental capabilities of the wanderer he found out in the middle of the plains, silently questioning:
"What does it think? What does it seek?"
Boon also heavily resembles an NPC met in-game by the Knight named Tuk. The two appear to be the same species of bugs, and both have giant backpacks and somewhat similar manners of speech; though Tuk's is a bit more coherent. In Tuk's Dream Nail dialogue she mentions that:
"Mmmnnnnnnngghhh... I'll find you again. The water will bring you to me. I just need to keep searching... and praying. When we meet again... I want you to say... that you're sorry."
The character mentioned in this dialogue is very likely Boon due to the obvious design similarities. Though it should be noted that Boon seems to have never ventured into Hallownest which could mean they met in the plains beyond.
Appearances of Boon in the comic.