Ultraman 80 is not the eightieth show in the Ultra series, it’s #9 and the last of the “classic” Ultraman shows, at least in Japan. (The name comes from being the first Ultraman show of 1980.) Hanna-Barbera tried the animated Ultraman: The Adventure Begins but only got to five episodes, later collected into a movie. America would try again in live-action with Ultraman: The Ultimate Hero but it oddly never aired in the US. (Japan got it as Ultraman Powered.) Australia even got into the game with Ultraman: Towards The Future (Ultraman Great in Japan), but Japan would have to wait until Ultraman Tiga to have their own Ultraman series again. I think they did get some movies in-between though. All of these are canon to the franchise by the way.
Ultraman 80 is secretly Takeshi Yamato, a schoolteacher for the first few episodes who believed monsters were formed by “Negative Energy”, the negative thoughts of humans. In this first episode Takeshi is trying to protect his students but his ability to see monsters before they show up makes him a laughing stock of the school…until he’s proven right.
Fun fact: According to the Ultraman fandom wiki there was an attempt to bring this show to America, with Adam West basically serving as 7 Zark 7 in how he would warn of monster attacks in new footage. Ultraman 80 would make further appearances in shows throughout the franchise, making his first return in Ultraman Mebius, and even more recently for the Ultra Galaxy Fight series on YouTube, which I’ve done as other Saturday Night Showcase entries previously.
I think this is the first Ultra to in essence have two secret identities. There’s his own ultra identity as 80 and his being part of the UMG in secret. I can guess why they dropped the school part early into the show.
If you want to watch the full series in the US you can get the home video from Mill Creek Entertainment or stream the series on Shout Factory TV’s TokuSHOUTsu project and other services that carry their shows.