Gabriel Black (緑川先生) is a novel-writer who lives in a "haunted" mansion. He has a few appearances in the anime series.
Gabriel is an eccentric friend of the Haruna family. He is an author who has written many books, particularly scary stories.
In his debut episode, Forrest, Laura and Kana (alongside a few Ham-Hams) take a trip to his mansion; only to be greeted by a large skeleton dancing at the door. While everyone was initially afraid, Laura eventually realizes that it isn't a real skeleton - to which Gabriel slides down the stairwell with glee, revealing he was controlling the skeleton. Later in the night, Gabriel leaves the house to "pick up a pizza"; however, he didn't return. Eventually, while Gabriel is still out, a "werewolf" sneaks into the mansion. To protect Laura and Kana, Hamtaro and the Ham-Hams attack the werewolf; which eventually reveals it was, once again, Gabriel behind the werewolf all along.
In the episode Office Adventures, the Ham-Hams were trying to help Gabriel when he couldn't come up with a new plot for a story. However, Gabriel eventually sees the Ham-Hams in his office, and starts talking back to them. The Ham-Hams initially enter a state of panic due to being "caught"; but Gabriel thinks he is only dreaming, so the Ham-Hams don't end up in any trouble.
Gabriel seems to intentionally resemble a gay stereotype; particularly in the English dub, where he has a cliché "gay accent". Some of Gabriel's language in the dub (such as the term "silly goose") were common stereotypical tropes around the time as well.