The Neronga "suit" used in the classic Ultraman TV series episode was worn by "Godzilla" suit actor Haruo Nakajima and was a modification of the Baragon suit, Baragon a monster appearing in the 1965 Toho film Frankenstein Vs Baragon(aka "Frankenstein Conquers The World").
Neronga eventually is confronted and killed in battle by Ultraman but gives Ultraman a decent fight. I've always liked the design of this monster and Neronga would go on to appear in other "Ultraman" series. I own a collection of giant monster toys including a Bandai figure of Neronga(5-6" inches tall).
Click the video below to see Neronga in action against "Gudon", the battle from an episode of the TV series Ultra Galaxy Mega Monster Battle:
Gudon vs. Neronga by ExOrochi
To see Neronga fighting Ultraman(in the '66 episode "Go Science Patrol!") click the below video: