Masters of disguise, these two blokes caused more than their fair share of foes problems.
Remington Percival Cord was a foreign ancient for the country of Offalia, using his abilities to attempt to subvert the America of Earth-One. However, he found a persistent foe in the Creeper, then later quarreled with Wildcat and finally schemed against eight members of the Justice League of America!
Mister X was himself a master of disguise who took on Earth-Two's Law Legionnaires, battling the seven members (and eighth honorary teammate Wing), escaping each confrontation during five encounters, until the combined team assembled to capture the crook. This criminal never had occasion to interact with fellow felon, and counterpart to the Creeper, Rag Doll... as he withdrew from crime after this case.