Herr Hemul, known as Mr. Hemulen, is a prominent Moominvalley resident. As a hemulen, he possesses tall stature, light gray skin or fur, a long protruding snout with a mouth at the tip, and no visible tail or ears. His distinctive attire includes a purple dress inherited from his aunt and dark brown shoes.

Initially an obsessive stamp collector, he completed his entire collection in "Finn Family Moomintroll," plunging him into an existential crisis. Following Snork's suggestion, he embraced botany as his new passion, meticulously collecting and analyzing plants. He resides in a dome-shaped house featuring a greenhouse packed with diverse flora and is often seen examining specimens with a magnifying glass.

His personality reflects typical hemulen traits: he values order, rules, and duty, often enforcing them with bossiness and insensitivity to others' views. Generally lacking humor, he nonetheless displays conviviality and high spirits. Eccentric yet well-intentioned, he cares deeply for friends like the Moomin family. He frequently converses with Moominpappa over tea and joins their adventures, though his enthusiasm sometimes leads to misfortunes like being chased by hattifatteners or enduring unintended disruptions to his home.

Beyond botany, he explores other hobbies such as firework making and bird watching, particularly after exhausting botanical discoveries. He identified at least two new plant species: an orchid provisionally christened *Hemulensus* or *Hemulaphormus*, and a glowing nocturnal flower found during an episode of insomnia.

Throughout the series, he adapts by shifting obsessions, yet retains core traits like his collector mentality, rule adherence, and occasional social clumsiness. He carries practical items like a pocket knife and maintains a close, though sometimes troublesome, relationship with Moominvalley residents.