Hassel is a descendant of a long line of Dragon-type Trainers in an unnamed faraway region. He ran away from home as a youth to pursue a dream of "making music", before becoming a member of the Elite Four in the Paldea region as well as an art instructor at the academy. Hassel is shown to be friendly, but very emotional, as he bursts into tears of joy when defeated by the player. He is an old friend of Gym Leader Brassius of Artazon.
During his bond story, a Dragon Tamer arrives at the academy to get Hassel back home, claiming his father, the head of the family, is feeling ill, and Hassel should be taking his place as the head of the family. Through interactions with the player, Hassel gains the confidence to confront the Dragon Tamer, realizing her words about his father's deteriorating health were just another attempt to get him to come home and swearing to stay teaching at the academy.
Upon the third unique interaction with Hassel in the League Club Room, he will trade an Arctibax to the player in exchange for almost any Pokémon excluding Shiny, Legendary, or Mythical Pokémon.
Hassel briefly appeared in Breathe Out. He was seen clapping alongside other teachers at Ohara's performance.
In Breathe Together, Hassel was seen teaching a class during the Naranja Academy presentation video. In the video, he appears speaking while his students were painting Gible.
Hassel debuted in PASV02. He and several other teachers were called to an emergency meeting by Clavell to discuss Violet, a new student that caused trouble during the Treasure Hunt's opening ceremony. Clavell informed the others of Violet's backstory and explained his behavior.
Trivia
The back vent on Hassel's coat could be in reference to the capes worn by Dragon Tamers, who Hassel has a history with, being a Dragon-type Trainer himself.
It might also be a nod to Clair and her design in Generation II due to how her cape resembles part of a suit.
Prior to the release of The Indigo Disk, Hassel was the only Paldean Elite Four member that could be rebattled indefinitely.
Hassel is left-handed, as shown when he throws his Poké Balls and in his official concept art painting a portrait of an Applin.
