Ultraman Leo is an alien from Planet L77 of constellation Leo. He grew up with his brother Astra on Planet L77. However, after Planet L77 was destroyed under the attack of Alien Magma, Black Giras and Red Giras, he escaped all alone to Earth. On Earth, he was living as a human being named “Gen Otori”, working at the Jonan Sports Center. When Ultraseven was driven into a corner by Alien Magma and others which appeared on Earth for invation, he transformed into Ultraman Leo and saved Ultraseven. From then on, he joined MAC, and took up the duty of defending Earth in place of Ultraseven who lost the ability to transform.