General Monster was once a member of the Nazis under Colonel Zol when the general was an officer during World War II. He joined Shocker but was killed with his body preserved. Years later he was revived and joined Neo-Shocker and turned into the gecko kaijin Yamarojin.
Due to a recent failure he was presented with the red eye, which signals that if he fails for a final time he will be terminated. He was executed by the Admiral Majin, after being defeated by Skyrider's Sky Kick. He can tear his tail off and uses it as a whip ("Gecko Whip"), his left hand is a giant gecko head with razor sharp teeth, he can throw the gecko feet like ears on his head as explosives, can rapid teleport, and finally create clones of himself "Yamorijin Clone Technique". He is revived by Badan Empire in Kamen Rider Spirits vol. 8, kidnapping people in Sapporo. He eventually destroyed by Kamen Rider ZX by Rider Spin Shot and crashed to Admiral Majin.
Yamorijin was later revived as part of the Second Generation Cyborg Corps (改造人間二世部隊 Kaizō Ningen Nisei Butai?, movie). They were destroyed by the 7 Riders. He was also resurrected as part of Kaijin the Second Generation Corps (怪人二世部隊 Kaijin Nisei Butai?, 27-28). They wore yellow scarves and were destroyed by the 7 Riders.