Dark Four Heavenly Kings

The Dark Four Heavenly Kings (暗黒四天王) is a group of four aliens serving under Alien Empera.

Ultraman Mebius
Founded by Alien Empera, the team's main purpose is to serve him in his conquest to invade planets. One of them, King Ark Bogar attacked multiple planets that rejected Alien Empera's leadership out of jealousy of the emperor until the latter sealed him in a black hole.

Soon in the series, his position was taken by Yapool, whom wanted revenge on the Ultramen and sees this as an opportunity. After his death by Mebius, Glozam and Deathrem tried to take actions but in the end their plots were foiled by Mebius himself with the help of GUYS and Ultra Brothers.

The last member, Mefilas manage to successfully brainwash Japan into thinking Mebius as their enemy and at the same time using a loophole in one of the Ultra Brother's policy (not to attack aliens that endanger humanity), causing the original Ultraman not to take any actions until his attempt to kill the hypnotized GUYS shattered his entire plan. Eventually, finding the odds uneven, Mefilas peacefully retreated which also resulted his demise by Empera as a punishment.

Ghost Reverse
Thousands of years passed and in the Monster Graveyard, the members of Four Heavenly Kings revived as ghosts. Ultraman Hikari joined them for unknown reasons and together captured Ultraman Taro and Ultraman Ace, forcing Mebius and Mechazam to go to the Valley of the Flames to retrieve the Giga Battle Nizer. Using the staff, they plan to revive Alien Empera by using his remains in Mechazam but Hikari revealed his treachery and with the three Ultra Brothers they put an end to the Four Heavenly Kings again, with Mebius forced to kill Mechazam out of guilt.

Members

 * King Ark Bogar (fired from duty)
 * Glozam
 * Deathrem
 * Alien Mefilas/Armored Mefilas
 * Yapool/Mebius Killer
 * Ultraman Hikari (Undercover)