"Because we obtained the third fire, a bright future in prosperity had been promised. However, for that reason, we must not forget the events that have knocked on something else's door". -- Opening naration

(The third fire is atomic power, after fire and electricity).

Agon (アゴン) was the first made-for-TV japanese monster, in a four-part sepiatone Japanese TV miniseries that was originally produced in 1964 by Nippon Denpa Eiga (Japan Radio Pictures) but wasn't actually broadcase until 1968 on Fuji TV from January 2 to January 8. The four-year-long delay involved a struggle with the show's sponsor. That delay allowed other giant monsters to make it to TV before Agon, including the monsters in Tsubaraya Production's series Ultra Q (ウルトラQ) and Ultraman (ウルトラマン) as well as Toei's Giant Robo (ジャイアントロボ,).

Toho Company Ltd. thought that Agon was a bit too similar to their monster Godzilla and threatened a lawsuit, but dropped it when they found out that Fuminori Ohashi, one of the creators of the original Godzilla costume, was working on the show. Toho later released Agon on home video in the mid-1990s.

Update: All four parts are here on YouTube:

Part 1 - https://www.youtube.com/watch?v=0TBtwIo50BE

Part 2 - https://www.youtube.com/watch?v=y5TsPmE4Dzo

Part 3 - https://www.youtube.com/watch?v=0YNwjJNqreo

Part 4 - https://www.youtube.com/watch?v=PLgyuEe-wbg