Mr. Hemulen is a hemulen living in Moominvalley. He traditionally wears a purple dress inherited from his aunt. His appearance features light gray skin or fur, a long snout, and hair tufts; he lacks visible ears or a tail.

Originally an avid stamp collector, he completed his collection in "Finn Family Moomintroll," triggering a personal crisis that led him to abandon philately. He then pursued botany with intense focus, meticulously analyzing flora using a magnifying glass and maintaining a greenhouse. His botanical work included discovering new species, such as a night-blooming glowing flower and an orchid named Hemulensus or Hemulaphormus. After exhausting available specimens, he transitioned to bird watching, reflecting the hemulen tendency for obsessive collecting.

His personality blends a love for order, rules, and duty with eccentricity and occasional social awkwardness. He lacks humor but enjoys convivial tea conversations with Moominpappa. Generally kind-hearted and eager to assist friends, his enthusiasm sometimes leads him into peril, like being chased by Hattifatteners or falling victim to Stinky's pranks that exploit his vulnerability. Despite occasional bossiness, he shows unexpected perceptiveness, such as understanding the language of Thingumy and Bob when others could not.

His background includes family ties to Moominpappa's upbringing; his aunt ran the orphanage where Moominpappa resided. He lives alone in a dome-shaped house surrounded by plants, including specimens like verdantus aboensis growing in unconventional places such as boots.

His development reveals adaptability in hobbies—shifting from stamps to plants to birds—while his core traits of collectivism and rule-adherence remain constant. He participates in Moominvalley adventures, often appearing as a well-intentioned but overwhelmed figure, an enduring yet gently pitiable fixture in the community.