From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Demon Realm (魔界, Makai; FUNimation "Demon Plane"), Demon Realm of Darkness (暗黒 の 魔界, Ankoku no Makai), or Devil Realm (悪魔界, Akumakai) is part of the macrocosm.
The Demon Realm was part of the Lower Realm. Like the Mortal Realm, it had four spatial sections. It was home to most of the Makai no Shuzoku (魔界 の 種族, Makai no Shuzoku) and led by a Makaioshin – the evil equivalent of a Kaioshin. Not much was said about the Demon Realm other than the fact that it was ruled by Demon King Dabura. He was the aforementioned Makaioshin, however, this was never confirmed as the term Makaioshin was not revealed until after the end of Dragon Ball Z in the Dragon Ball: Sūpā Ekisaitingu Gaido.
In the Dragon Ball anime, Shula, another "King of the Demon World", managed to open the Demon Realm Gate between the Demon Realm and the Mortal Realm on Planet Earth. He kept it open for some time by wedging his cursed sword in its door. Son Goku later pulled out the sword and once again closed off the entrance to the Demon Realm.
- Demon King Dabura – Originally king, but taken away after falling under Babidi's spell. He was later killed by Majin Boo in 774 Age.
- Gola – Shula's minion
- Melee – Shula's minion
- Shula – Referred to as "King of the Demon World" in his appearance.
- In Japanese Buddhism, the realm of demons is called Makyo (魔境, Makyō; Literally meaning "Devil’s Cave").
- In "Pay to Win", when Babidi asks Dabura if he has any preferences about which planet he wants to fight, Dabura responds, "Perhaps a planet similar to this one. I don't want unfair advantages." The planet Dabura and the Z Warriors are transported to looks strikingly similar to the one seen in the flashback of "Eighteen Unmasks", and may be the location of the Demon Realm.