Alien Bat is a recurring antagonist in the Ultraman franchise, first appearing as the final antagonist of Return of Ultraman before returning as the main antagonist of Ultraman Saga.
Return of Ultraman
Alien Bat appears in the final episode, coming to Earth with the intention of conquering it. To deal with Ultraman Jack, Alien Bat brought along the one monster who had defeated an Ultra, Zetton.
Alien Bat's first move was to abduct two friends of Ultraman Jack's human host, Hideki Goh, Rumiko and Jiro Sakata. Bat then tormented Goh's dreams with visions of Ultraman being defeated by Zetton.
As Goh confronted him in a stadium, Bat unleashed Zetton to attack Japan. Goh tried to transform, but Jack was too fearful to face off against Zetton. Bat proceeded to order Zetton to destroy the city he was in along with MAT's base, to further mock Jack.
MAT attempted to stage an attack on Alien Bat, but they were unable to do much as Bat grew giant to join Zetton in causing havoc. However, Ultraman Jack, inspired by MAT's bravery in facing Bat, regained his courage and allowed Goh to transform into him so he could face off against Bat. In a tough fight, Jack managed to kill bat by impaling him with the Ultra Cross, before destroying Zetton with the Specium Ray, proving that an Ultra could defeat Zetton.
Alien Bat reappears as the main antagonist of this film. He recovered Zetton's corpse from the Monster Graveyard and fused it with Sphires to create Hyper Zetton. Bat then proceeded to abduct most of the population of an alternate universe Earth so he could use their despair to fuel Hyper Zetton, plotting to use Hyper Zetton to bring death to the universe and become god.
Bat sent Gomess and Gubila to terrorize the survivors on the alternate Earth so he could use their fear and despair to power Hyper Zetton. After the two kaiju were fought off by Ultraman Cosmos and Ultraman Zero, Bat killed the two to punish them for their failures. He then unleashed Zetton in its larval stage, Giganto Zetton, to fight the Ultras. Zero and Cosmos were soon joined in their fight by Ultraman Dyna, and together they were able to destroy Giganto Zetton. However, Bat then merged himself and his fortress with Giganto Zetton's remains to form Hyper Zetton. Initially pummeling the Ultras, the three managed to even the odds by merging into Ultraman Saga, allowing them to match up. As the fight between Hyper Zetton and Ultraman Saga headed into space, Hyper Zetton was destroyed by Saga with the Maximum Saga, killing both Zetton and Alien Bat.