Hedorah , also known as the Smog Monster, is a kaiju monster who first appeared in Toho's 1971 film Godzilla vs. Hedorah. The huge monster was named for Hedoro (へどろ), the Japanese word for sludge, slime, vomit or chemical ooze.

Godzilla vs. Hedorah is a 1971 Japanese kaiju film directed by Yoshimitsu Banno, with special effects by Teruyoshi Nakano. Produced and distributed by Toho Co., Ltd., it is the 11th film in the Godzilla franchise, and features the fictional monster characters Godzilla and Hedorah. The film stars Akira Yamauchi, Toshie Kimura, and Hiroyuki Kawase, and features Haruo Nakajima as Godzilla and Kenpachiro Satsuma as Hedorah. Satsuma would go on to portray Godzilla in later Godzilla films.