Ragon, who showed up in Ultra Q in episode 20. the Science Patrol knows this, and tries to calm him with music. he's also got a bomb attached to him, so they can't shoot at him.
the whole Ultra Q issue had to be handled with the dubbing differently, since the first show hadn't been aired in the US. so they couldn't name the beast and had to explain the use of music in a different way.
it worked pretty well, overall. this was the first really humanoid monster that Utraman has to fight, and it's due the radiation that it has grown so much and become hostile. it also has developed a beam weapon, which slows Ultraman down for at least a small amount of time.
perhaps. we never see him explode, so I like to think the radiation wore off and he went back to a peaceful existence under the sea.
it's a cool suit, with just enough difference from the Gill-man to be spot on as a giant monster.