A group of villains published by
DC Comics. The Crime Syndicate first appeared in
Justice League of America #29 in 1964.
In the pre-Crisis days, there were multiple universes, each with a different set of rules. There was Earth-1 where most of the major DC heroes (Superman, Batman, Wonder Woman, etc.) resided. There was Earth-2, where the Justice Society of America lived. And in 1964, Gardner Fox introduced Earth-3.
On Earth-3, things were radically different. Europe was discovered by explorers from the Americas. John Wilkes Booth, the then president, was killed by Abraham Lincoln. Similarly, the heroes that we had come to love had become villains. The group of villains went by the name of the Crime Syndicate and held sway over the entire world.
The group consisted of five villains, led by Ultraman, an odd Superman counter-part, who gained new abilities each time he was exposed to kryptonite. Other members included Superwoman (an Amazon like Wonder Woman, who had turned to crime), Power Ring (a Green Lantern doppelganger), Owlman (a non-powered detective and genius similar to Batman), and Johnny Quick (a speedster with powers similar to the Flash, but not to be confused with the Johnny Quick of the Justice Society). These villains held their world in fear and nothing presented a challenge, so they decided to try and take out both the Justice League and the Justice Society to have new worlds to conquer. Unfortunately for them, they were defeated and left in the limbo between the different dimensions.
Members of the Crime Syndicate escaped over the next few years but were always returned back to their prison. On one of these missions, the first hero from Earth-3 emerged to battle them. Lex Luthor, a genius designed a battle suit and used his genius to try and bring justice to his home world.
During the Crisis on Infinite Earths, the group along with their dimension was destroyed by the massive anti-matter wave that was sweeping the multi-verse. This appeared to be the end of the Crime Syndicate, though they were later attributed as to having come from the anti-matter universe of Qward.
Later, the Crime Syndicate was reintroduced by Grant Morrison in the graphic novel JLA:Earth Two. Retitled the Crime Syndicate of Amerika, the world they came from was an opposite world from our own where evil and crime were virtues. The JLA from Earth-1 attempted to help combat them, aiding that world's Lex Luthor, but soon realized that they could not effect change to such a radically different world. The group has made a number of appearances since their reintroduction.