Owlman is the name of several fictional supervillains that appear in comic books published by DC Comics who are the intended reverse counterparts of Batman. Owlman first appeared in Justice League of America #29 (August 1964), and was created by Gardner Fox and Mike Sekowsky. He was created as an evil version of Batman because owls are known to prey on bats.
Thomas Wayne, Jr.
The Owlman character was revived (along with his teammates) in the late 1990s for modern DC continuity in the graphic novel JLA: Earth 2. This Owlman was developed to be reflective of the modern readers with a far darker attitude and background than either of the two previous teams. On antimatter Earth, Owlman was now Thomas Wayne, Jr., the older brother of that reality's Bruce Wayne. In most mainstream DC universes, Batman's genesis occurred when young Bruce Wayne was witness to the murder of his parents, and was inspired to devote his life to fighting crime.
In the antimatter universe, however, young Bruce was killed along with his mother by a policeman when Thomas, Sr., refused to accompany him for questioning. Thomas, Jr., escaped the crime scene with the hoodlum Joe Chill, whom he considered his hero, and grew up to become Owlman. Equipping himself with a utility belt containing technology and weapons similar to those used by Batman along with possessing a drug-enhanced high intellect (devoted to crime rather than serving the law), Owlman became a master criminal and an ally to Boss Gordon (the antimatter Earth's version of James Gordon).
Later, he learned that his father, Thomas Wayne, Sr., was still alive and had become the chief of police in their world's version of Gotham City, gathering a cadre of police officers who did not give in to the rampant corruption which infested their version of Earth. Thomas, Jr., blames his father for the deaths of his mother and brother and it is strongly hinted that the main purpose to his criminal career is to punish his father, who is well aware of who he is and is equally determined to destroy his own son. During his visit to the "main" DC Universe, upon discovering the Waynes' grave, he states that nothing matters because "he's dead", presumably referring to Thomas Wayne, Sr., and actually shows a rare moment of pathos as he kneels in front of the grave.
While antimatter Clark Kent (as Ultraman) is the leader of the Syndicate, Thomas, Jr. (as Owlman), is the real brains behind the group. The working relationship between the two is extremely tense, due to Ultraman's desire to rule the planet through fear and violence clashing with Owlman's more pragmatic desire to allow dissent and rebellion to run rampant (going so far as to funding opposition towards the Syndicate) in order to provide himself and his allies in the Syndicates enemies to fight.
Further complicating things is the fact that Thomas, Jr., has carried on a longtime affair with Ultraman's wife Superwoman. Ultraman is aware of the affair, but due to Thomas, Jr., having undisclosed photographic blackmail material against the villain, he is unable to seek retribution against Owlman for the betrayal.
In JLA: Earth 2, the antimatter Alexander Luthor, a heroic version of Lex Luthor, makes a reference to Owlman's "drug-enhanced" cerebral cortex, although this version of Owlman does not demonstrate any superhuman powers. Presumably, Thomas, Jr., merely uses some sort of drug to enhance his mental capacity though it is not specifically stated how powerful his mental powers are or how they are enhanced through such artificial means.
Thomas, Jr., and his antimatter Crime Syndicate allies appeared in the weekly Trinity series, starting with issue #9. The "Weaponers of Qward" had attacked their Earth, killing millions and tearing apart the landscape. The Syndicate had kidnapped hundreds of innocent people from all 52 realities, including what appeared to be Jimmy Olsen, but was later revealed to be his anti-matter duplicate. It is unclear if Thomas, Jr., allows the JLA to win in order to get the heroes off his source Earth and counterattack after they depart, or if he was actually defeated.