He was a comic store owner, artist, and online blogger who created the character, The Dark Defender (superhero).
Denny often clashed with a fellow blogger named Benjamin Alvaro.
When The Bay Harbor Butcher was revealed to the public to be someone who was killing other killers, Denny tried to create a comic book series based on the Butcher, whom he renamed as The Dark Defender. Before the series went into production, however, his rivalry with Benjamin Alvaro escalated. Alvaro went to his store and bashed Denny's head with a snow globe, killing him.
Dexter worked the crime scene and was drawn to a poster of The Dark Defender comic book cover. Later, while at a NA meeting, Dexter fell asleep. He dreamed that he was The Dark Defender, and rescued his mother from her killers.