Alien Empera

Alien Empera is the leader of the Empera Army and the primary antagonist of Ultraman Mebius, as well as the true main antagonist of the Ultraman Showa continuity as a whole.

He is one of the most powerful foes the Ultras have ever faced and among the biggest threats in the galaxy in the Ultraman franchise.

Origin
Alien Empera was among the residents of a planet that would later be called Dark Planet. When the sun on his planet went out, its inhabitants began dying. However, one single being managed to survive by embracing the darkness, becoming Alien Empera and developing a hatred of light.

Ultraman Taro
Almost 30,000 years before any of Ultra Brothers went to Earth, Alien Empera sparked the Great Ultra War by leading an army of aliens and monsters to take over the Land of Light in Nebula M78, the home of the Ultras. While he succeeded in doing so, the Ultras fought back against his forces. The final battle of the war occured when Alien Empera dueled the Father of Ultra. The battle ended in a tie, with both fighters received a matching scar on their hips that would reminded them both of the intense battle. The injuries Alien Empera sustained forced him to retreat.

Ultraman Mebius
Prior the events of the show, Alien Empera opened a Space-Time Wave to lure aliens to Earth. starting with a herd of Dinozaurs. The Emperor's return was heralded when the predator Bogal was lured to Earth and began reviving and summoning several monster to Earth, such as Sadola and Twin Tail. Following Bogal's destruction at the hands of Ultraman Hikari and Ultraman Mebius, other Bogals, known as "Lesser Bogals," opened an Ultra Zone, a gate way to the Monster Graveyard. With the Ultra Zone opened, Alien Empera slowly began a reviving process starting with Yapool and hid his existence by creating and using gigantic robot, Inpelaizer once Yapool was cut off from Earth. However while Inpelaizer's strength was more than what Mebius could handle, it was felled by both Mebius and Ultraman Taro.

Alien Empera then assembled a team of his top generals called the "Four Heavenly Kings". The quartet was comprised of Yapool, Grozam, Deathrem and Alien Mefilas. The four took turns trying to destroy Mebius. Yapool, Deathrem and Grozam were all defeated, while Mefilas realized he couldn't defeat Ultraman Mebius and Ultraman Hikari and retreated, only to be killed by Empera for his failure.

Upon his arrival, Alien Empera trapped the sun in a coat of darkness and sent his Inpelaizers to attack different regions of the Earth. However, Mebius destroyed the Inpelaizers with his Mebium Dynamite attack. The Emperor sent two more Inpelaizers down to Earth but they were destroyed by GUYS and Zamsher, who came back to Earth to settle his unfinished business with Mebius.

Alien Empera then decided to take over Earth himself. Empera destroyed most of Tokyo and encased the Earth in darkness after declaring his vengeance against the Father of Ultra for their battle 30,000 years prior. Zamsher attempted to stop Empera, but the Lord of Darkness's strength proved to much for the space samurai. Hikari equipped the Aarb Gear and attempted to assist in defeating Alien Empera, but his attempt proved as successful as Zamsher's and he was blasted to ground next to him. The two resolved to work together to stop the Emperor, but even with their powers combined, they were unable to stop him. Empera then turned his attention to the GUYS base, and fired a Darkness Fear at it to destroy both it and Mebius. However, Zamsher took the hit instead, sacrificing himself to save GUYS.

Hikari attempted to stop the Emperor with Zamsher's Hoshikirimaru, but he soon succumbed to exhaustion and vanished. Believing Hikari and Serizawa to both be dead, Ryu angrily attempted a kamikaze attack against Alien Empera, but the Emperor destroyed the ship with a single shockwave. However, Hikari managed to save Ryu by taking him on as his new host. Hikari tried to attack the Emperor with his Hikari Blade, but the Emperor avoided his attacks and blasted him back. Not willing to let his friend be killed, Mirai stopped recuparating and transformed into Mebius to fight Empera. Mebius and Hikari combined and fired their attacks at Alien Empera, who blocked them with his cloak. The Lord of Darkness the unleashed his signature attack, the Rezolium Ray, against Mebius, destroying the Ultra Warrior.

However, the eight Ultra Brothers continued their offensive to destroy the Emperor's darkness casing around the sun and telepathically told the GUYS members not to give up hope. Mirai was also revived by the Knight Brace in a spiritual form, allowing him to merge with GUYS and Ultraman Hikari. Together, they formed Mebius and granted him a new form, Phoenix Brave Mode. The Emperor tried to attack Mebius, but his attacks were deflected back at him. Mebius then fired a Mebium-Knight shot through the GUYS' final METEOR, the Specium Redoublizer, and at Alien Empera. Zoffy also arrived and joined in, firing his M87 beam through the amplifier to help Mebius.

However, Alien Empera still managed to stay standing. Mebius then launched a Mebium-Knight Dynamite at Empera, fatally wounding him. As he died, Empera realized that the bond between the humans and Ultras was what allowed them to defeat him and accepted his fate, dissipating into light.

Ultraman Mebius Gaiden: Ghost Reverse
After being revived, the Four Heavenly Kings attempted to revive Alien Empera by merging the Giga Battle Nizer with the Emperor's essence in Mechazam. This plan was thwarted when Mechazam allowed Mebius to kill him, wishing to die as himself rather than bring about the return of Empera.

Trivia

 * Unlike other monsters in the Ultra series, "Empera" is not the name of Alien Empera's species.