Comic book supervillain owned and published by DC Comics. He was created by writer Robert Kanigher and artist Joe Kubert, and he made his first appearance way back in October 1947's Flash Comics #88.
The character's story starts all the way back in the 19th century with James Craddock, a boy forced into poverty when his father abandoned him and his mother. Craddock was told by a fortuneteller that he'd grow up to become a highwayman -- so he decided to just give in to his prophesied fate, took on the name Gentleman Jim, and started robbing people. He ended up traveling to America where he ran afoul of some heroic gunslingers known as Nighthawk and Cinnamon. Craddock got hanged by Nighthawk -- but he rises as a ghost, doomed to undeath until his killer eventually dies and moves on to his heavenly reward.
Unfortunately, Nighthawk and Cinnamon used to be known as Prince Khufu and Chay-Ara, ancient Egyptian royalty. They've been getting reincarnated together for centuries, have never passed on to their heavenly reward, and probably never will. So that means Craddock was trapped as a spirit forever -- which he shouldn't mind so much, as it's gotta be better than Hell. Nevertheless, he continued to hold his grudge, even when the gunslingers were eventually reincarnated as the Golden Age superheroes Hawkman and Hawkgirl. While he's tangled with plenty of other superheroes, including Batman, the Flash, the Atom, and Stargirl, he's always been a primary nemesis of the Hawks.
In his first appearances, Craddock's ghostly nature was questionable. He was using devices to simulate his ghostly appearance and powers, but future retcons made him an actual ghost with real powers. He could become insubstantial and invisible, and his usual (incredibly stylish) appearance was an invisible man wearing a white highwayman costume with a top hat and monocle. He could also cause some mundane items to appear out of thin air -- for example, an old highwayman's pistol to use against a foe who was immune to his ghostly powers. He was also able to teleport and track psychic energy, and the only reliable way to disrupt his incorporeality was with Thanagarian Nth metal -- coincidentally, the substance that gave Hawkman and Hawkgirl many of their abilities.
Around 2006, during a JSA storyline, Craddock gained the ability to summon and control other ghosts, but that ability hasn't been used since then. During the same storyline, it was revealed that he couldn't touch virgins, but this came off as super-creepy, and it hasn't been used since then. During the same storyline, it's said that he can only be harmed by those with royal blood. This has been disregarded because it's honestly silly.
During the ill-regarded 2011 reboot of the DC Universe called the New 52, the Gentleman Ghost got two different origin stories. First, he was a living man who stole a magical item called the Mortis Orb, which gives him the power to resurrect and control the spirits of the dead. A later origin said he'd been cursed by a witch, which is totally a thing that happens sometimes.
The Gentleman Ghost appeared in "The All-New Super Friends Hour," voiced by Alan Oppenheimer, in "Justice League Unlimited," voiced by Robin Atkin Downes, and in "Batman: The Brave and the Bold," voiced by Greg Ellis. He appeared in a non-speaking role in "The Lego Batman Movie." And he showed up in several computer games -- "Batman: The Brave and the Bold -- The Videogame," "DC Universe Online," and "Lego DC Super-Villains."