As superheroic double-acts go, it's hard to beat Superman and Batman. The combination of the Dark Knight's detective skills and the Man of Steel's power makes for a serious one-two punch that puts most villains down for the count. Individually, Superman and Batman are enough to keep any villain on their toes, and any villain who can take on both of them needs power to spare.
And to take down these two DC icons, some villains had brought the iconography of Batman and Superman together to form Composite Superman.
The Composite Superman has a number of incarnations, but he debuted in 1964's World's Finest Comics #142, by Edmond Hamilton and Curt Swan. After Superman saved a down-on-his-luck diver named Joseph Meach, he gave Meach a job as a janitor at the Superman Museum. Although he felt bitter towards Superman, Meach was on the job when a bolt of lightning struck an exhibit about the Legion of Super-Heroes and somehow passed the collective powers of the Legion onto Meach.
Drunk on his newfound power, Joseph sought a chance to defeat Superman, Batman and Robin in one fell swoop. Using his newly-acquired shapeshifting powers, he gave himself green skin and created a costume that was half-Superman and half-Batman. Dubbing himself the Composite Superman, he left messages in the Batcave and the Fortress of Solitude, summoning them to a cave in the mountains. Once the heroes arrived he gave them an ultimatum: either the Composite Superman became the newest member of their partnership, or he would reveal their secret identities to the world.
After a series of rigged tests and attempts by the heroes to outwit him, the Composite Superman finally had enough and was about to reveal their secrets when his powers wore off, leaving him a disgruntled custodian once more.
However, it's hard to keep a good villain down, and Composite Superman returned with the help of Xan, an alien who had a grudge against Batman and Superman for imprisoning his father. In 1967's World's Finest #168, by Carey Bates and Curt Swan, Xan found Meach working at the Superman museum and restored his powers.
This time around, Xan and the Composite Superman were able to trap Batman and Superman and started to turn half of their bodies into anti-matter. During this process, the Composite Superman's powers wore off once more, and Meach reverted to his human form. Overcome with remorse for his actions as the Composite Superman, Joseph threw himself between Xan and the World's Finest just as Xan fired at them. After Meach sacrificed his life with that noble act, the heroes erected a statue of Joseph, stating that while he lived as a villain, he died a hero.
While that was the end of the Silver Age version of the Composite Superman, the imagery of the villain would be used a few more times in the pages of Jeph Loeb and Ed McGuinness' Superman/Batman, where the Toyman's giant mech suit was a massive visual tribute to the Composite Superman.
The actual Composite Superman himself was reintroduced in Len Win and Joe Batista's Superman/Batman Annual #3, where he was a creation of mad scientist Professor Ivo. In that story, the Composite Batman is the sum of two degrading clones of the respective heroes who cling to life by combining. When the real Batman and Superman confront him and tell him that he needs to choose which one of them to help, this Composite Superman couldn't handle the conflicting impulses in his head and is quite literally tore apart by his emotions.
Even though Composite Superman has a distinctive visual and combines the powers of some of DC's most formidable heroes, this bizarre character stands as more of a novel curiosity than a legitimate threat, and only time will tell if the Composite Superman can live up to the reputation of either one of the suits he wears.