Lewis LeBeau first appeared as one of the Joker's henchmen. Later he served as Harley Quinn's favorite and most loyal Quinntet, but she murdered him when he inadvertently interrupted her plan to arrange a romance between two private investigators who were after her.
When Harley ended up dying and being sent to Hell, she was re-united with Lewis, who she was very happy to see again. As it turned out however, he and the rest of her gang had been stuck in an infinite loop of attempting to survive a SWAT team assault led by the deceased and demonically-appointed Detective Pettit. Despite the hopelessness of the situation, Harley refused to stay in Hell, and so she rallied her Quinntets and sought to have them all escape Hell. After several failed attempts, Harley and her team manage to reach the River Styx and nearly escaped Hell. Unfortunately, they were being pursued by the Hell-enforcer, Ulysses Highwater, who ended up killing Lewis when he took a bullet for Harley. With his dying breath, Lewis told Harley not to give up hope.
Although Harley managed to escape Hell eventually, it's presumed that Lewis is still there.