Gaia was named by Gamu in episode 3 after the Greek personification of the Earth and Gaia hypothesis. Although Gamu is consciously in control of the giant, there are times when Gaia would exert his own full strength due to his dedication to the human beings and Earth. Gaia's forms includes:  Ultraman Gaia is voiced by Takeshi Yoshioka (Gamu Takayama's actor) in the series and by in "Ultraman Boy no Urukoro". The change of color in his Gaia Breastar in V2 is due to designer Hiroshi Maruyama's wish for a black coloration in a titular Ultra Warrior. Said color is inspired by the black tea. His mouth is designed after the B Type suit of Ultraman.   is the supporting character of the series. He is that was born three years earlier than Gaia in the Alchemy Star's base of Pronon Calamoth. His true purpose was to guard the Earth from the threats of Radical Destruction Bringer but was sidetracked from his human host (Fujimiya)'s misguided ideology and fought Gaia on certain occasions. After realizing his mistake, Fujimiya surrendered Agul's light to Gaia but regained it from the Earth at the height of Σ-Zuiguru's invasion. It was at this point the two started to fight on the same side and eventually faced against the Radical Destruction Bringer's minions at the series' finale arc. His forms include:  Ultraman Agul is voiced by Hassei Takano (Hiroya Fujimiya's actor) in the original series and by in "Ultraman Boy no Urukoro". His name officially appeared in episode 16 after the Roman letters "AGUL" appeared on the screen from Fujimiya's flashback. In real life, Ultraman Agul is named by the coined word for the English words "aggressive" and "agreement", as well as the Japanese word . His mouth is designed after the B Type suit of Ultraseven. In the original planning, Agul was meant to disappear but his and Fujimiya's eventual return was decided after finding the character's increasing popularity.    is portrayed as a mysterious force that aimed to destroy humanity from Earth by sending monsters from wormhole. Its existence was predicted by sorcerer Kijuro Mato from 500 years prior and eventually led to the foundation of G.U.A.R.D. and its branch XIG. Having foreseen the arrival of Earth's guardians (Gaia and Agul), it was responsible for deceiving Fujimiya into viewing humanity as Earth's enemies.