Dantalion oversees the Pandemonium Library as head librarian, marked by his youthful visage and striking blue rabbit ears. Though his exact age is unstated, estimates based on the library’s vast collection position him among Pandemonium’s eldest entities, possibly existing for millennia.

His overwhelming bibliomania drives him to read ceaselessly, claiming familiarity with every volume among billions in the collection. This obsession leads to frequent exhaustion-induced sleep during work, conversations, or even while standing—often after nocturnal reading marathons.

Physiologically, he transforms monthly for three days surrounding the full moon, shifting from a delicate, boyish form into a tall young man—a stark contrast to his usual appearance.

His personality merges profound wisdom with an enigmatic curiosity. He possesses a unique gift for instantly matching individuals with ideal books, demonstrated when he pinpointed Mullin’s literary preferences moments after their meeting.

Within Pandemonium, he maintains a friendship with Azazel and interacts with Molech, whom he addresses as "Senpai" yet comfortably commands—frequently using him as a stepladder to reach high shelves. Molech complies willingly despite seniority. Eurynome’s attraction to his youthful form shifts when she witnesses his adult transformation, an event that triggers her amnesia.

No concrete details exist regarding his origins, pre-Pandemonium history, or significant character development across documented media, leaving his background largely unexplored.