Ace was a German Shepherd dog originally owned by an engraver named John Wilker. He was found by Batman and Robin after his master was kidnapped by a gang of counterfeiters. With his master unable to fight off the kidnappers, Wilker's dog jumped to his defense. Ace put up a savage attack but was beaten into unconsciousness by the thugs. Disoriented but determined to rescue his master, the brave canine dove into the river in search of Wilker. While on patrol that night, Robin spotted the dog struggling in the water and joined Batman in plucking the dazed animal from the river. The dog soon recovered its energy and Bruce Wayne put an ad in the newspaper, believing that someone would recognize the brown german shepherd with the distinctive diamond patch of fur on his forehead. The grateful dog raced the Batmobile out of the Batcave on a subsequent outing and, rather than return him, the Dynamic Duo took him along. Batman used Ace to try to locate Wilker. Because he had already placed the "lost dog" announcements for Ace in his civilian identity of Bruce Wayne, he was concerned that anyone recognizing Ace (who had a prominent star-shaped marking on his forehead) might make the connection between Bruce Wayne and Batman. To forestall that problem, Robin hastily improvised a hood-like mask for the dog that incorporated the bat emblem as a dog tag dangling from Ace's collar: "I cut him this mask from our black cloth toolbag ... and made a bat-symbol for his collar." The dog proved his worth immediately when he zeroed in on an escaped convict at a carnival. "Look," motioned Robin. "He's got Bowers by the coat-sleeve, holding him in true police dog style." Bowers' own cry of dismay ("Leggo you -- you BAT-HOUND!") officially gave the newest resident of the Batcave a name.

Meanwhile, a response to the advertisement had revealed the dog's true name and origin. A neighbor explained that the missing John Wilker had "bought this trained dog because he lives alone and is away from home all day". While Bat-Hound used his acute sense of smell to help Robin locate a missing child, Batman began his investigation of Ace's missing owner.

The trio reunited at the site of a paper theft and Robin was startled when Ace suddenly began snarling. Batman had already suspected that the thieves were connected with John Wilker's abduction and Bat-Hound's reaction clinched it. Wilker, it turned out, was an engraver and the Dark Knight theorized that his kidnappers hoped to force him to counterfeit money. The Dynamic Duo caught up to the bandits when they were stealing ink from the Eastern Printing-Ink Company only to be taken captive.

Creating a makeshift Bat-Signal in the sky above the villains' lair, Batman was able to get Ace's attention. The Bat-Hound came running, nudged open a window with his nose, and bit through Robin' bonds. The trio of crimebusters made quick work of the would-be counterfeiters.

Predictably, a reporter on the scene of the mop-up couldn't resist pulling off Bat-Hound's mask and immediately connected Ace with Bruce Wayne. Holding a photo of himself, Bruce Wayne and Ace, Batman explained that the millionaire had simply loaned him the dog as a favor. Unknown to all, the Batman in the picture was actually Alfred.

As they bid John and his pet farewell, Batman commented, "He's a great dog, Mr. Wilker. It was HE who really saved us."

"And if you ever want to be a Bat-Hound again, Ace," Robin added, "the position is open."

Ace returned to the Batcave, on loan from John Wilker to help the Dynamic Duo capture a gang using a trained dog to commit a series of diamond robberies. A two-way radio on Bat-Hound's collar enabled Batman to eavesdrop on the bandits and issue commands to Ace. For the next three years, Wilker continued to loan his pet out on occasion. Bat-Hound had the opportunity to appear with Batman and Robin in a movie, track down a deadly explosive, and pursue a "fugitive" Batman .

Wilker later took a new job that that would keep him on the road and make it difficult for him to take care of Ace, so he left the dog to Bruce Wayne. Wilker was never aware that Ace was the Bat-Hound or that Bruce Wayne was Batman. Bruce Wayne happily agreed to take permanent responsibility for Ace. Batman added another component to Ace's costume, a "tiny receiver" within the dog's collar that emitted a high-pitched signal whenever Bat-Hound was needed. Batman also created a device that would enable Ace to pull his mask over his head at his convenience.

Soon after, Bat-Hound was stricken with that hoariest of plot devices -- amnesia. His memory fogged when his skull was grazed by a masked gunman, Ace developed a deep hatred of all masked men -- including the Dynamic Duo. After rescuing their pet from a group of thugs who'd taken command of Bat-Hound, Batman arranged for Ace to have an operation to restore his memory.

In short order, Bat-Hound met the other members of the burgeoning Batman family, notably Batwoman and Bat-Mite. At one point, in fact, the other-dimensional imp bequeathed Ace with Krypto-level super-powers, but a side-effect of the spell made Bat-Hound susceptible to the commands of others -- including criminals. After realizing that he'd made Ace the pawn of a gang of thieves, Bat-Mite restored the dog to normal.

The dog first appeared out of nowhere to the 130-year-old Indian shaman Black Wolf who had been cast out of his tribe for not agreeing on executing the descendants of U.S. soldiers who had wronged them in the past. Blind and alone, Black Wolf took comfort in his newfound canine company, seeing its arrival as a sign. Later, Batman appeared and saved Black Wolf from assassins of his tribe. Taking Black Wolf and the dog with him, he tracked down the assassins and hindered the executions. When Black Wolf decided that it was time for him to die, the dog remained by Batman’s side.

Batman named the dog Ace and entrenched him in the Batcave. Occasionally Ace would use his tracking skills to assist in Batman’s cases, but mostly, he stayed in the Batcave in the company of its resident technician, the mute Harold Allnut, who delighted in creating mechanical toys for the hound. When Bruce Wayne's back was broken by Bane, and Jean-Paul Valley took over the identity of the Batman, Ace took up permanent residence in Harold's quarters.

When the Cataclysm earthquake destroyed most of Gotham, Harold and Ace left the scene. Harold later returned and was killed by Hush after betraying Batman, but Ace's current whereabouts are unknown.