Lex Luthor

Lex Luthor is the founder and CEO of LexCorp, as well as one of the three richest men in the world and likely enemy of Superman.

Arkham Knight Incident
At some point, Luthor attempted to buy Wayne Enterprises' Applied Sciences Division for a billion dollars, only to be repeatedly given implied refusal by the company's head, Bruce Wayne. Luthor also had some ambitions to run for President of the United States, with part of his platform being to deal with the problem with metahumans. At least one member of the Militia agreed enough with Luthor to publicly vow to vote for him. Comments by the Militia also implied that he had been involved in funding them as well as Scarecrow's terror attack due to his having designs for Gotham City.

Batman: Arkham Knight

 * "Mr. Wayne, Lex Luthor calling. Apologies for going via your direct line but I grow tired of these games. LexCorp has made a very generous offer for Wayne-Tech's Applied Sciences division, yet your persistent unavailability begins to look less like a busy schedule and more like antagonistic behaviour"

Trivia

 * Lex Luthor's interest in acquiring the Applied Science Division of WayneTech was most likely a reference to the DCAU three-part episode "World's Finest", where Bruce Wayne, the secret identity of Batman, went to Metropolis to discuss a business deal with LexCorp.
 * In the DC comics, Luthor was the arch rival of Superman who first appeared the Action Comics in April of 1943. Since both Lex Luthor and Superman existed in the Arkhamverse, it's most likely that they both fought.