A very powerful being from the now destroyed Nebula L77 in the Leo constellation. Leo lived in peace with other members of his species, who were extremely similar to the beings from Nebula M78 including his pet Ron and younger brother Astra. However, this world was at war with the Alien Magma, skilled swordsmen that kill for sport. At the same time on Earth, Alien Valkie's appearance at the end of Ultraman Taro's time on Earth signaled that the third age of monsters was over and there would be a third age of aliens beginning. After the Magma destroyed L77 with Leo, Astra, and Ron as the only survivors a Magma agent was sent to Earth with two biological experiments, Red and Black Giras. Ultraseven was sent to intercept them, but the monsters were too powerful for him to handle. Leo arrived on earth to prevent the agent from destroying Earth, and after fighting them in three battles, soon defeated the Gillases and forced the Magma agent to flee.
Afterwards, Seven was stranded on Earth after the Ultra Eye was broken in the first fight, and suffered great injury to his right leg. Leo made a human body for himself as Gen Otori and would soon join Seven and Dan as members of MAC with Dan as captain. Over many months Leo would fight creatures of all shapes and sizes, mostly from outer space, including his pet Ron, who he had to let go and sent him into space. Seven trained Leo to become stronger and smarter during battles in order to defeat his opponents. Over time, Leo became more successful, especially after his brother Astra was revealed to still be alive and assisted him against two monsters named Littre and Garon. Leo's impressive skills to kill monsters and aliens with only his body and rarely using beam attacks was enough to get attention of Ultraman King, the supreme ruler of M78. After the defeat of Alien Pressure, Leo was given the Ultra Mantle, which would help him against many bizarre aliens and beasts for months to come. Some time after the Ultra Eye was sent for repairs and Leo helped recover the Ultra Key from Alien Babarue, rewarding him and his brother Astra as members of the Ultra Brothers.
Soon afterwards, Black Directive, a ruthless leader from a large frontier world, set his sights on Earth. Commander Black used Saucer Monsters, bizarre creatures from the astroid world he would send to attack Leo and was capable of destroying MAC and some friends Leo made as Gen. Devastated by their loss, Leo managed to exact revenge by killing the first Saucer Monster, Silver Bloome. However, each Saucer Monster that was sent was destroyed by Leo time and again. After Nova, Commander Black's renegade Saucer Monster, was defeated by Leo, he hired help from an arrogant, joking mercenary by the name of Alien Bunyo. Unlike other aliens and monsters before him Bunyo successfully killed Leo, but Ultraman King arrived to revive him. After Bunyo was destroyed, Commander Black unleashed the most powerful of all Saucer Monsters, Black End. Black End would prove to be one of the most difficult monsters Leo ever faced, but thanks to the help of some children Commander Black was over powered and Leo soon managed to kill Black End. After the defeat of Commander Black, Leo used the Ultra Shooting Beam to destroy the asteroid world. With no more any threats to the Earth, Leo could leave his mission without worries. Leo (as Gen) bids farewell to the children, the Miyamas and Toru and he decided to travel to unknown places. He headed off for M78 with his brother Astra and presumably Ron, as well.
Ultraman Leo returns in Ultraman Mebius episode 34: A Man Without a Home to help Ultraman Mebius fight Alien Reflect, an alien that had defeated Mebius in their initial encounter, and stated that he would return later to kill him and destroy the world.
Leo (as Gen) is displeased with Mebius's performance in the fight with Alien Reflect and refuses to accept him as the defender of Earth. He calls Mebius out, initially without revealing his identity, and the GUYS crew meet on the island that was once destroyed by the Gillas. Disguising himself an old man visiting the memorial of those who died, Gen tells Mirai that this is a place he will never forget- because in his first battle many people were sacrificed here. He then reveals himself to be Ultraman Leo and transforms. Ultraman Leo then challenges Mirai to one-on-one combat, and after a brief but heavy clash between the Ultras, Leo easily defeats Mebius. As Gen, Leo asks Mebius and his comrades that he sees Earth as his home, and that he was testing the younger champion to see if he could defend it well. Even though Ultraman Taro accepts him as the defender of Earth, Leo admitted, he doesn't accept Mebius as the other Ultras do. As Ryu tries to tell him, Mirai stopped him. Gen asked him that his tears can help to save the Earth, so he gives him some robes in order to train him.
Back at the CREW GUYS station, Teppei discovers, according to Document MAC, Leo lost many battles against different Aliens. However, after each rematch, he easily beat them. The GUYS members realize and understand why Leo appreciates Earth so much, as, unlike Ultraman Mebius who calls the Land of Light his home, Leo's home was destroyed. The only place he has to go back to is Earth. Teppei later reveals that Leo taught him how to destroy Alien Reflect- with a move similar to the legendary Leo Kick. However, Leo can jump up to a thousand meters to deliver the blow, and Mebius cannot. Ryu later finds out why Leo gave him the robes- and offers to help Mirai train. Mirai, however, says that he wants to do it alone, just like how Leo fought alone. Nobody, he says, should ever rely on others.
And thus Mirai started to train. After managing to break many sticks by kicking them, he found himself completely exhausted. Ryu appeared, along Komoni and Teppei, and they decide to use the poles to make a bonfire. Teppei forgets to bring the matches to make fire, but Ryu says that they aren't necessary. Using a stick, he started to make fire like they had before the advent of technology. Mirai, shocked by how well it worked, was inspired to create a new move. A moment later, a message from Captain Serizawa arrived that said that the Alien Reflect had appeared again, and everyone departs for the field of battle.
After they all arrived, Mirai wanted again to fight alone, and he suddenly materialized as Mebius to fight the Alien Reflect. At the time of the fight, Gen was watching from below. Mebius started to fight him, and after launching a kick at the Reflectorian, he starts spinning like the technique Ryu used to make fire, and managed to break one of Reflectorian's shields. But suddenly, the alien captured one of the ships from GUYS, and if Mebius moved, he would have killed them. Rapidly, Gen transformed into Leo to assist Mebius, and he helped Mebius free the GUYS ship. They both combined their forces to defeat the Reflectorian, and, combining the Leo Kick and Mebius' new technique Mebium Drill Kick, they destroyed the alien once and for all. Mebius later then met with Leo, and Leo accepted that not only Mebius, but Crew GUYS as well can now protect Planet Earth.
Mega Monster Battle: Ultra Galaxy Legends The Movie
Leo appeared in this film as Ultraman Zero’s trainer during Zero's exile. Leo and Zero would battle continuously on a barren planet with Zero wearing Techtor gear armor which made him incredibly slow, much to Zero’s annoyance but Leo insisted that it was necessary for Zero’s training. Then when Seven’s eye slugger was sent as an S.O.S. Ultraman King sent Zero to the battle, followed shortly by Leo and Astra. When they arrived Zero had already defeated Belial and blasted him into a river of molten magma, but no sooner had they arrived, the spirits of 100 monsters started to flow towards Belial and formed the gestalt megamonster Beryudora. Leo and Astra then did their combo attack, while every one else attacked Beryudora on their own until Zero finished him off. Leo then returned to the Land of Light with the others.
Ultraman Zero The Movie: The Revenge of Belial
Ultraman Leo reappeared in this movie.
Ultraman Leo appeared to save M78 from Darklops Zero and also appeared in the beginning of this movie
Ultra Galaxy Legend Gaiden: Ultraman Zero vs. Darklops Zero
Leo would then travel in between dimensions to rescue Zero, who was sent there by Darklops Zero along with the Imitation Ultra Brothers. After destroying the Imitation Ultra Brothers, Leo helped Zero get to the dimension with Darklops Zero to continue their fight. After Darklops Zero and the dimension was destroyed, Leo was seen flying away with Zero.
At the Land of Light, when Ultraseven realized that his son had traveled to another universe, Leo walked by asking what was wrong. Then, 3 more Ultras, Ace, Ultraman (original) and Jack appears thinking that it might have a relation with a mystery disk as some of the dead kaiju from the kaiju graveyard had been taken away.
Ep39, a cutscene from from the film Ultraman Saga; Before the climatic battle against Hyper Zetton, the evil Alien Bat unleashed 5 other monsters: Antlar, Pandon, Tyrant, Black King and Velokron, each more powerful than before. The Ultra Brothers: Ultraman, Seven, Jack, Ace and Leo transformed into their Ultra forms in the Land of Light and flew to the alternate Earth to help Ultraman Zero. Ultraman Leo fought against Tyrant, who after giving him powerful damage, Leo used his signature move, the Leo Kick, and kicked Tyrant, killing him and destroying him in the process. As a matter of fact, Leo is the only of the Ultras that didn't fight against a monster from his own series, but rather, Ultraman Taro's.
- Even though Tyrant first appeared in Ultraman Taro's show, Ultraman Leo replaces Taro in the battle against Tyrant, since Leo was a pupil of Ultraseven and a trainer of Ultraseven's son, Ultraman Zero. Leo had important roles in material featuring Zero.
Ep102, showing him training the later Ultraman Zero, who happened to not be wearing the Techtor gear armor.
Dark Spark War
Prior to the Ultraman Ginga tv series, Ultraman Leo participated in the Dark Spark War, but this time he fought not only alongside with the Ultra Brothers but, with the other Ultras that came from other universe and their allies against Evil side. While in their midst battle, Dark Lugiel turned every Ultras alongside their allies, monsters and aliens into Spark Dolls. With the war over an unknown warrior appeared and faced Dark Lugiel but like others he also turned into Spark Dolls. The location of Leo's Spark Doll is unknown. After Lugiel's destruction, Leo was restored like the other combatants and returned home.
Ultra Fight Victory
After Ultraman King sensed the awakening of the Space Emperor, he calls on Ultraman Hikari, Ultraman Ace and the Leo brothers.
Leo and Astra were sent to Planet Guar on the orders of King, to stop the revival of Juda. However, Yapool sent his Choju Battalions, Verokron, Doragory and Vakishim to take care of them while Ultraman Victory was taking care of Victory Killer and Lunaticks. Leo first took on both Verokron and Vakishim whilst Astra took on Doragory. The Brothers' battle was interrupted by the arrival of Yapool. He place the Victorium Core into the distortion on Planet Guar, which started to revive Juda Spectre. Ace, Ginga and Victory arrived and gave the brothers breathing time with a combination of Ace's Punch Laser, Ginga's Ginga Cross Shoot and Victory's Victorium Shoot. Yapool then joined his Choju. Leo took on Vakishim once again and he and Dorogory were defeated with a combination of the Leo Kick and Astra Kick.
When Juda was revived, he sent down his new and upgraded monster: Super Grand King Spectre. Leo and Astra once again used their two kicks, but they were repelled by the robot. As Victory Knight went up to challenge Juda himself, the Brothers, Ace and Ginga restrained Grand King. When Juda was defeated, it left Grand King immobilized, giving the Ultras an opportunity to finish him off. By using Ace's Metallium Ray, the Leo Brothers' Ultra Double Flasher and Ginga's Ginga Cross Shoot, they were able to defeat the monster.