Before the First Crisis
One day, someone kidnapped an engraver named John Wilker and his pet dog Ace got thrown into a river. Batman and Robin found the dog and as Bruce Wayne, Batman put out signs that he had found the dog. Later, Batman and Robin found out it was Wilker's dog. Batman needed Ace's help in finding Wilker, unfortunately Ace had a star shaped mark on his forehead and if anybody saw Batman with the same dog that Bruce Wayne has then they might find out Bruce Wayne is Batman. To hide this tiny flaw, Batman put a hood over the dog's head to hide the mark and a bat collar too. Together they found the kidnappers and Ace jumped on one of them making him name Ace ("Get off me you..you Bat-Hound!"). Later, Wilker got a new job and because he couldn't take care of Ace, he left him to Bruce Wayne.
Ace had appeared many times in Batman stories, in one of them Batman and Robin were both captured so Batman alerted Ace by using a switch on Batman's boot heel. Ace got the signal and put on his hood (don't ask me how) and went to Bat woman, she knew instantly by Ace's barking that Batman was in trouble. Ace followed the trail to the hideout and while Batwoman freed the Dynamic Duo, Ace chased after the bad guy ,Ace followed him and came across a cliff. So he knocked down a nearby tree to make a bridge. He crossed it and captured the bad guy.
In the story 'Formula for Doom', Ace saves Robin from a bad guy who was about to cut Robin in half using a tree cutting vehicle. Later, the villain of the story and Batman confront on a snowy mountain, he threatens to drop the beaker of formula and blow them both. Ace saves Batman by catching the formula before he drops it.
After the Crisis
After the first Crisis, Ace the bat hound was rarely seen, as Bat-Hound anyway. Ace seems to go through a range of different species in the few appearences he made, he is supposed to be a German Shepherd dog. During Knightfall, when Jean Paul Valley took over as Batman, he was building his new bat suit and Ace smelled him from behind. However, Ace got scared and went to Harold for dog food. This time Ace was a Bulldog. Ace's next appearance was in the Misfits storyline, when a group of second rate villains ( Chancer, Calendar Man, Killer Moth and Catman) kidnaps Mayor Krol, Commissioner Jim Gordon and Bruce Wayne, Robin had to accept help from Nimrod. Nimrod figures out where the kidnapped victims were and Robin uses Ace to sniff out the area. This time Ace was a Bloodhound not a German Shepherd.
Ace wasn't seen since No Man's Land when an earthquake completely leveled Gotham, the Wayne Manor and the Batcave were destroyed. Ace was never seen again and it's possible that he died in the rubble. A traditional Bat-Hound was seen recently in Limbo with all the forgotten characters.
In the relaunch, Bruce went out an adopted a black Great Dane similar to the Beyond Ace, although named Titus.
Ace the Bat-Hound has been given a brand new origin in Batman Annual #1. Ace now has a far darker origin, since he was one of the Joker's many dogs. Joker abandoned them, so Ace had no alternative but to kill if he wanted to survive. Alfred rescues him and eventually restores him to health. As a matter of fact, Alfred named the dog Ace. Bruce thought Ace would never recover due to the way the Joker treated him. However, Ace recovers and Bruce calls him Ace the Bat-Hound!
Ace on Television
On Batman Beyond, Bruce Wayne has retired and Terry McGinnis, a teenager is the new Batman under the guidance of Bruce Wayne. On the show, Ace was formerly owned by a shadowy dog fight gambler named Mr. Boxer. He used Ace to fight with other dogs, one night Ace escaped from a fight and into the streets. An elderly Bruce Wayne was visiting his parents grave when a member of the Jokerz gang attacked him. Ace saved Bruce from the punk and Bruce took Ace in. Terry and Ace were not always in good terms. Some time later, Boxer used genetically enhanced dogs to try and kill Batman and Ace saved Batman from being eaten.
Later in the episode 'Splicers', Ace helps Dr. Cuvier who has developed a splicing technique that gives humans animal attributes (he can make you look like a snake or bull, or give you eyes like a tiger). After he was wanted by the police for attacking D.A. Sam Young, Batman went after him with Ace. The Doctor injects himself with his own serums turning him into a python-cat-human hybrid. Batman fights the monster with a little help from Ace. Unfortunately, the Dr. had to make a detour due to his explosive finale. In the same episode, Ace warms up to Terry gains his affection.
Krypto: The Superdog
In the kid-friendly TV show "Krypto the Superdog," Ace appears as Bat-Hound in the series. Bat- Hound and Krypto has often teamed up in the series. Batman has not appeared in the series but he is mentioned, in instances where Ace prefers to be called as Batman's partner instead of his pet. He once helped out Krypto when he was powerless due to Red Kryptonite exposure. He also investigates a case with Krypto about a group of rats stealing valuable objects, all whom were controlled by Catwoman's pet Isis. Most of Ace's enemies are based of Batman's enemies like Joker's pet hyenas Bud and Lou, Penguin's birds and Catwoman's pet cat Isis. They villains themselves do not appear. Bat-Hound and Krypto also battle Dogwood, a dog/plant hybrid who serves as Poison Ivy's animal counterpart.
As for Ace's gear, he has a storage room filled with gadgets. He once lend some to Krypto to make up for losing his (Krypto's) powers temporarily. Ace also rides in a jet powered glider and a collar/belt that holds various gadgets: Bat Ropes, Batarangs and ink pellets for paw print autographs.
Batman the Brave and the Bold
Ace appears in the episode "The Legend of the Dark Mite" battling Catman and a tiger. Batman rewards him with a treat. Afterwards, Bat-Mite poses as Ace to learn that Batman thinks lowly of him. At the end of the episode Batman checks to see if Ace's real to find he is. Ace also makes a short appearance in the episode "The Plague of the Prototypes" as Proto-Bot's companion. Proto-Bot watches over him and it may be possible that Proto-Bot is Ace's guardian.