The Riddler (real name Edward Nygma) is a major antagonist in the DC universe, first appearing in Detective Comics #140. Arguably one of the greatest enemies of Batman, the Riddler is a dangerous, as well as a psychotic criminal, with the obsession and tendecy of creating riddles, hence his name, to confuse, or to test his rivals's intellience and expert strategy. He is one of the most famous villains, not accounting DC, but in fiction in general. He is also a major player in the Non-Disney vs. DC Villains War.
Non-Disney Vs DC Villains War
The Riddler is approached by Kent Mansley, as the latter requests him to explain about the way, that the Arkham City works, to understand it's enviroment and methods. The Riddler provides the CADMUS' associate, with all the information he required. Unfortunately, their discussion is overheard by a police officer, who revealed to be the Baroness in disguise. She then breaks into the Riddler's household, along with some reinforcements, capturing the two villains, and bringing them forward to her superior, Cobra Commander. There, the Commander forces them to bow to his submission, as he reveals them his all mighty power, by summoning an army of clones in the process, much to their horror.