Dark's background is a mystery, although he refers to being raised in a strict religious upbringing. When asked if he reads the Bible, he replies, "I've had every page, line, and word read at me, sir!" Another, perhaps more fitting interpretation of the Bible sequence, given his dismissive nature to Charles and his array of books, would be that he is mocking Charles' belief that the Bible would have any sort of effect in either repelling or hurting him.
This would indicate that Dark is not a devil or demon in the Christian sense of the term. He died by growing old when he was on the magic carousel.
Mr. Dark is the leader of the Autumn People and he initially holds sway over the other main characters, but his power weakens when Charles uses positive emotions against him, something that he cannot comprehend or withstand.
Mr. Dark is a gaunt, sinister man with pale skin and black hair who bears tattoos all over his body, one for each person successfully tempted into joining the Dark's Pandemonium Carnival that he founded and runs. He is always seen wearing a black suit and matching top hat.
- The character of Mr. Dark was parodied in the popular science fiction show, Rick and Morty, in the form of Mr. Needful in the episode, "Something Ricked This Way Comes."