The first Red Dart was John "Midas" Mallory, who donned a costume to become Star City's latest hero. He was later revealed to be a villain similar to Deadshot.
The second Red Dart was an unknown prisoner in Belle Reve who bought the name and equipment from the first Red Dart and started a mostly unsuccessful career. His greatest feat was the theft of Kyle Rayner's Green Lantern Ring (while Rayner was unconscious) in the middle of a prison riot and gave it to Prometheus to analyze, on the eve of Maggedon's attack. He returned later the ring, on Prometheus' orders.
The New 52
In the rebooted DC Universe, Red Dart is a woman armed with trick darts and a member of the Longbow Hunters, a team of villains assembled by Richard Dragon. She teamed with Brick and Killer Moth in an attempt to collect a three-million-dollar bounty on Green Arrow, which they intended to split three ways. Although the trio put up a considerable fight, they were defeated by Green Arrow and his half-sister, Emiko.