Dexter was committed after birth to the Napier Institute for the Congenitally Disabled, a humane home in Gotham City for people such as Dexter, and a research facility to discover the causes and prevention of profound birth defects.
In time, Dexter discovered he could project his "astral form" at will, and through this power studied the real world. He actually "sat in" on university lectures in spirit form...to learn. Developing psychokinesis, he would invisibly read books (onlookers, seeing "floating, open books," thought the libraries were haunted). Eventually, Dexter learned to create a "handsome, deep-voiced man" illusion for his projection, combining the illusion with the P-K to make it look like a normal man reading books. Dexter’s favorite work of fiction was "Alice in Wonderland." He felt like the Cheshire Cat, who could "stand on the outside, looking in with amused impunity."
By dint of fate, the institute fell under the directorship of an unscrupulous man who, with his new, hand-picked staff, abused the patients and embezzled the institute’s money.
Infuriated, Dexter used his powers to create a new projection: The Cheshire Cat. Looking like a tall man in dark Victorian clothes and cloak, but with the head of the Cheshire Cat (as in Tenniel’s illustration), The Cheshire Cat gathered evidence against the new director, using the power of teleportation to send evidence to a new Washington DC FBI "White-Collar Crime Unit," and to The Joker. The latter was as intrigued at the Cat’s ability to send evidence to his Funhouse as he was by the criminal allegations.
With the FBI and The Joker closing in, the director and his cronies tried to flee, only to be forcibly detained by the Cheshire Cat in his full, intimidating, enigmatic glory.
The Cheshire Cat fought crime, especially white collar corruption, using his unique PSI powers (which included psychometry). Who could suspect that such an amazing being was really the mental projection of an ossified institution patient?!?
The Joker, who knew Dexter’s secret, sponsored The Cheshire Cat for JLA membership. He was a key player in the JLA's first confrontation with Brainiac.
The Cheshire Cat’s personality was aloof and quietly arrogant, but sympathetic to the suffering of the innocent--a combination that quickly led to frustration with his peers in the Justice League and extreme interest on the part of The Patchwork Man. Dexter and The Patchwork Man talked several times, and The Patchwork Man showed Dexter a fragment of the dark part of the collective unconscious which he drew his power from. Dexter was horrified and realized that The Patchwork Man was only a symptom of a far deeper and more profound evil; one that could only be removed through drastic means. Dexter soon came to the conclusion that only he had the will, the vision, and the ability to save the soul of humanity. And the only way to do that was to simply erase its darker aspects at the source.
His megalomania now shifted in a terrifying new direction, The Cheshire Cat destroyed the Napier Institute, killing everyone present, and removed his body to a secure location. From there, he quickly gathered incriminating material on prominent politicians and blackmailed them into serving him and providing him with the information he needed on the psionic research The Patchwork Man did for the U.S. government under Project: Faustus. He soon learned that this information could only be accessed by the President of the United States. The Cheshire Cat then caused accidents incapacitating the President and Vice President, making Speaker of The House Raymond Pelt acting President. Under threat of blackmail (and also believing The Cheshire Cat's sincere promise that he was only trying to destroy The Patchwork Man), Pelt obeyed to his wishes, instituted Martial Law, re-opened the psionics lab and ordered the staff to assist The Cheshire Cat in anyway he requested. Captain American quickly uncovered this plot, but he was no match for The Cheshire Cat who nearly killed him.
With Captain America out of the way, Dexter and the scientists at the lab began to modify a powerful, experimental psionic amplifier. The Cheshire Cat planned nothing less than to overwhelm the collective unconscious with his augmented will and remold its baser instincts, banishing hate, anger, jealousy and fear forever from the collective human ideascape. The modifications on the device were nearing completion when he was informed that the JLA was planning to heal Eisenhower. The Cheshire Cat went to the hospital and stalled the JLA until the modifications were complete and then returned to his lab to set his plan into motion.
Unfortunately, Dexter's understanding of the nature of the collective unconscious was fundamentally flawed and he radically overestimated the extent of his own power. In the end, he would have merely driven hundreds of thousands of people insane before the psychic tides ripped him to pieces. Luckily, thanks to Mentalon and The Amazing Ghost Fighter, who had tracked him back to the lab, it never got that far. By disabling one of the psionic amplifier's beam emitters, AGF diminished Dexter's power just enough that he was quickly ravaged by the energies of the collective unconscious before he could try to reshape it through force. Mentalon was able to prevent the energy feedback from destroying the lab, but the damage to Dexter was already done.
In his last moments, Dexter realized what he had let his arrogance and The Patchwork Man turn him into. His last, sad, resigned, words before he died were, "I only wanted to make the world a better place...."