The following info is from home.iu.net/~jsewell/FAQs/Ultraman-FAQ.html

Ultraman is the generic name for a series of Japanese live-action television shows produced between 1966 and 1998. Each series focused on at least one extraterrestrial "Ultra-hero" who arrives on Earth to fight various large monsters. Conveniently, each Ultra-hero can grow to over 200 feet tall. Each Ultra-hero had various energy emission powers, plus were experts in some form of hand-to-hand martial arts-style fighting. Virtually all of them also had one weakness: their energy would run out after a short time fighting. (Strangely enough, when this happened, they tended to "get serious" and use their most energy-draining attack on the monster(s).) When they weren't fighting monsters, they typically assumed the form of a human; each one either created their own human form, or merged with one (or, in one case, two) humans.