Although they look identical, even having the same first and last names, the two Johnny Thunders were anything but the same. On Earth-Two back in the 1940's, Johnny was the first recruit of the Justice Society of America, where he along with his Thunderbolt fought crime and even big time supervillains. Although he possessed tremendous power, his intellect was his chief liability. However, it was trumped by his drive to help his fellow man. Well, as long as he made a name for himself, at least. Then in the 1950's, Thunder retired to become the monarch of Badhnesia, the land he lived in as a little boy when their past leader kidnapped him.
In fact, the same thing occurred in the early years of Earth-One's Johnny Thunder, who grew up and followed an entirely different course life. Becoming a low-level criminal who led his own gang, when he first met his visiting and naïve counterpart, he saw the opportunity to steal his Thunderbolt and remake his native world as Earth-A with its Lawless League. However, before they could establish themselves as the conquerors of Earth-A, the Justice Society of America defeated both the League and its leader, who reset history so that these events never occurred.
Then, several years later it occurred that the good Johnny once more wanted to me his doppleganger, and traveled to Earth-One. Since neither Thunder remembered their last meeting, events unfolded as they had previously, only this time the evil Johnny recruited the Crime Champions to be his hired muscle rather than his own gang. However, his own carelessness led to his cosmic twin reversing all that Thunder had accomplished when he placed all of Earth-One's heroes into a coma and nearly vanquished the Society through his Champions. Left defeated once more, this time evil Johnny couldn't escape capture, and was left powerless, while good Johnny remained a member of the Society in good standing into his old age.