Hopper 2, created by Shocker to defeat Kamen Rider 1. Ultimately, they team up to defeat Shocker's cyborg soldiers at their island base and rescue the girl. The new villians are ultra-cool too: Spider, Bat, Cobra and Snake appeared in this movie.
Kamen Rider 2 has Shocker's emblem on his back, evidence that he was under Shocker's control.
Check out Kamen Riders group shots.