Hiroshi Tsuburaya, who played the KCB director Tabata, is the grandson of Ultra Series creator Eiji Tsuburaya.
Trope Trivia
Contest Winner Cameo: Episode 40 "I Want to See Gaia!", in which a boy named Taro is given the opportunity to visit XIG Aerial Base, was part of a contest where kids could have a chance to appear in an episode of Ultraman Gaia.
Died During Production: Hiroshi Tsuburaya passed away in year 2001, but was absent in the OV Once Again Gaia, just months before his passing where his character, Tabata, was written to have left for Bosnia. Its possible that he was written out due to his actor already being sick by that point.
She Also Did: Maria Theresa Gow, Georgie's actress who also happens to be a singer herself, covered the series' theme song in 2021 on her YouTube channel.
Irony as She Is Cast: Takeshi Yoshioka was cast as Gamu, the Badass Bookworm protagonist, for his athleticism, due to Tsuburaya looking for an athletic actor to play the protagonist for easier filming of untransformed action scenes.
Pop-Culture Urban Legends: A piece of fan art depicting Gaia and Agul standing beside a third, green, ultra has sparked rumors that the series was originally going to have a third ultra. This third ultra (dubbed Ultraman Lucifer by the fans) would have, supposedly, been the manifestation of the Sky to compliment Gaia's Earth and Agul's Sea.
Promoted Fanboy: Chiaki Konaka and his brother Kazuya grew up watching Ultraman shows so they worked together in producing Ultraman Gaia, although they worked on different projects separately including a few other Ultra shows, according to Chiaki's notes on Guilmon inDigimon Tamers (whom he put some Kaiju influences in too).
The second COV was made from a completely different suit than the original, allowing the producers to later modify it and the baby COV into Shazak and its child.
Meemos was created using the head and legs of Apatee and the torso of Algyuros.
The veins on Gan Q's zombie form in Episode 31 "The Accursed Eye" were reused from the Volcanic Veins of Fire Golza from Ultraman Tiga.
Rukulion was heavily modified to create Sigma-Zuigul.
Reality Subtext: Commander Ishimuro (Hiroyuki Watanabe)'s role as a mentor and a father figure to Gamu (Takeshi Yoshioka) echoes how, behind the scenes, the former offered to coach the latter's acting to help him get used to playing Gamu.
Romance on the Set: Hassei Takano (Hiroya Fujimiya) and Yukari Ishida (Reiko Yoshii) married each other. The couple and their daughter made a cameo in the 2008 film Superior Ultraman 8 Brothers.
Underage Casting: 15-16 year-old Maria Theresa Gow as 19-20 year-old Georgie Leland.
What Could Have Been: Fujimiya and Agul were originally meant to be Put on a Bus with episode 26 "The Final Resolution", but their surprising popularity from the fans allowed them to return in Episode 36 "The Sky of Reunion".
One of the Writers, Hasegawa, wanted to introduce a new Ultra after Fujimiya planned departure, but when it was decided to bring Fujimiya back they scrap the idea, there wasn't much laid out before it was scrapped besides the Ultra in question being Catherine Ryan.