Koenma, usually just called that rather than his full name King Enma Jr., is the son of Enma, who runs the spirit realm. He's best known for recruiting Yusuke Urameshi as the spirit detective. Mayumi Tanaka voices him in Japanese, while Sean Teague handles the English dub for Funimation (with Brianne Siddall and Eric Stuart taking over for the first and second movies respectively). His name basically just means "little Enma"—a combo of his father's name and the Japanese word for child.
Despite looking like a toddler and constantly getting teased about it, Koenma is actually over 700 years old and knows a ton about how the universe works. He's mostly played for laughs and comes across as pretty cowardly most of the time, though he'll genuinely step up if Yusuke or the others are in real danger. He's a decent leader overall and generally likeable.
His main job is deciding which spirits go to Heaven and which go to Hell—something his father King Enma used to handle, but he's always away on business trips. Koenma can transform into a teenage form when he gets self-conscious about his appearance. He's got a "Jr." mark on his forehead and constantly carries a pacifier in his mouth that stores his spirit energy. When he releases that power, it creates the Mafukkan, Spirit World's ultimate defensive spell. How much energy he channels through it determines which demons he can seal—by the Chapter Black arc, he can handle S-class demons without breaking a sweat.
Koenma created the Spirit Detective program himself and feels personally responsible for it. When Shinobu Sensui tries to merge the human and demon worlds, Koenma takes it hard, and he's willing to suffer alongside Sensui for eternity as penance when he unleashes his Mafukkan on him. He also betrays his own father by siding with Yusuke after the Spirit Defense Force wants to execute him for being part Mazoku, though he eventually returns to the spirit realm. In the manga, he actually overthrows Enma after discovering his father deliberately let demons into the human world to stir up conflict.
Content compiled by AnimeList.moe from publicly available sources.
