The super-powered criminal named Dr. Light was actually the second person in the DC Universe to use that name, although Light is his real surname and he is a true doctor. The first was a scientist named Jacob Finlay, who was Arthur Light's fellow researcher at S.T.A.R. Labs. Finlay created a highly advanced suit that allowed him to control the light spectrum, including creating blinding displays and deadly lasers. Becoming a DC Super Hero for a brief time, he was accidentally killed by his partner Arthur Light in the early days of his heroic career. Arthur then took the suit for himself and became the new "Doctor Light," but instead of a hero, he became a small time criminal. He now found himself haunted by Finlay's ghost, or at least what he thought was his ghost. He used the powers of the suit to fend off Finlay's spirit, which was driving him mad.
Doctor Light first makes himself known by fighting the recently formed Justice League of America. Although the team were fairly new at the time, they quickly defeated Light, who had cooked up a scheme where he captured the League with light rays, and then sent the Leaguers to different worlds based on their weaknesses. Over the next several years, he consistently fought the JLA, and always was humiliated by Earth's Greatest Heroes. Green Lantern Hal Jordan even defeated him without the help of his teammates.
It was during this time, humiliated by many defeats at the League's hands, that Light managed to sneak on board the JLA Satellite to steak back his weapons. The League was on a mission at the time, and the only person on duty was Sue Dibny, the wife of the Elongated Man. He brutally raped her; and when the League returned, they furiously attacked him. Although some members wanted to kill him for what he had done, their laws against taking a life prevented them from crossing that line. Instead, several members chose to alter Light's mind with Zatanna's magic spells, so that Light would no longer pose a real threat. This act, however, accidentally gave him a partial lobotomy, resulting in much of his intellect gone, and his becoming a bumbling fool.
With his mind now wiped of the events on the JLA satellite, but subconsciously realizing that maybe fighting the League was a dead end, he decided to take on their former sidekicks, the Teen Titans. He joined together with four other criminals and together they formed the Fearsome Five. But Light kept bungling their plans to defeat the Titans, so the other four members drove him off the team. During this time he was so inept, that he was even defeated by the non super-powered kids called Little Boy Blue and the Blue Boys. Adding further humiliation, his name and costume were used by a Japanese woman named Dr. Kimoyo Hoshi, who became a hero and Justice Leaguer.
Partially driven by self-doubt, and partially driven by the ghost of his former partner Finlay (who may have been a manifestation of that doubt), Light volunteered for the Suicide Squad, in exchange for a reduced sentence. Partially on the advice of the ghost of Finlay, Light then tries to be a hero, or at least, become a better person. While on a mission with the Squad on the planet Apokolips, Light is quickly killed by a group of Parademons. Light's soul then winds up in Hell, but his constant whining so annoyed the demons who ruled there, he was again returned to life and sent back to Earth
Not long after coming back to life, Light becomes trapped in a Green Lantern power battery, and in turn is temporarily transformed into living light, making him that much more powerful. When Sue Dibny is murdered, he becomes the prime suspect by the JLA, due to his sexual assault on her years earlier (in truth, the culprit was the Atom's ex-wife, Jean Loring). He regains his memories and more sadistic nature that was taken from him during this period, but the knowledge that he is a sexual predator makes him hated even among other Super-Villains.
The Spectre brings down final judgment on Doctor Light, and burns him to death by turning him into a candle, using his head as the wick. His corpse is subsequently reanimated by the Black Lantern Corps during the event known as the Blackest Night.
In the post-FLASHPOINT timeline, Arthur Light is a scientist working with the government organization called A.R.G.U.S., as well as their own Justice League of America. While he is examining a communicator used by the Secret Society of Super Villains, he is engulfed in a huge explosion of light, which leaves his body transformed and crackling with light based energy. He becomes an unwilling member of the government sponsored JLA, but is killed in action on one of his first missions. He later returns, claiming that while his body is indeed dead, he now exists as a construct of living light energy. This version of Doctor Light was actually a family man, and had a wife and two daughters.