Saying that Batman has a lot of villains is an understatement. The Caped Crusader has a ridiculous number of enemies. Ever since taking over the spotlight in Detective Comics #27, Batman has encountered a very long list of enemies to fight and defeat. Some recurring and quite memorable, others rather uninteresting and forgettable. But in recent Batman comics, the character has settled to a specific gallery of rogues, whom he battles over and over again.
But before this set gallery became the norm, the list of recurring Batman enemies was thin. Only a few characters were known to appear in more than one issue, let alone back-to-back issues. Some didn't appear again much later, but left enough of an impact to be considered a classic rogue at the time.
10 Doctor Death
A character that has not aged well in popularity with fans, Doctor Death is, for true Batman fans, the very first super-villain Batman fought in the history of the comics. Making his first appearance in Detective Comics #29, Dr. Karl Hellfern or Dr. Death as he is later dubbed, is the very first member of Batman's rogues gallery. He not only returns in later issues, but is even re-introduced into the New-52 continuity, assuring his importance as a Batman rogue and as a comic-book villain overall. Although, as previously mentioned, he is not well known, he is still the very first villain to become a part of the rogues gallery.
9 Dr. Hugo Strange
The psychotic psychologist, Dr. Hugo Strange was the second Batman villain to join his rogues gallery. First appearing in Detective Comics #36, he was nothing more than a mad scientist who used his intellect to commit crimes. From lighting machines to growth formulas and fear-inducing powders, Strange wouldn't be associated as a psychiatrist (albeit a fake one in reality) until later years after resurfacing from his apparent death in Detective Comics #46. Before then, he was the first batman villain to cross-over from Detective Comics to Batman #1. He is, one of Batman's classic, lasting foes.
8 The Joker
Yes, the Joker - Batman's arch nemesis - was one of the very first villains to fight the caped crusader in the history of comics. He made his first appearance in Batman #1, along with Catwoman, as a serial killer who murdered his victims with "Joker-Venom." He was apparently supposed to die in that first issue, but editors at DC Comics wanted him to stay, a move that proved fruitful during later issues. His famous origin story was even revealed in Detective Comics #168, during a flashback issue that told the story of the Red Hood. It's safe to say, when the Joker shows up, he tends to stay.
7 Catwoman
As previously mentioned, Selina Kyle, or Catwoman, first appeared alongside the Joker in Batman #1, but wouldn't be referred to as Catwoman until Batman #2 (although she was first known as "The Cat"), and fans wouldn't see her in costume until Batman #3. That's three back-to-back issues where Catwoman's character is being explored.
A thief who was purposely designed to not be a killer or evil, compared to some of Batman's other foes at the time, since she was meant to be a love-interest for Batman. The choice to associate her character with cats, was made because Bob Kane and Bill Finger believed cats were the antithesis of bats. A choice that, most definitely defined the character when compared to Batman.
6 Clayface (Basil Karlo)
First appearing in Detective Comics #40, the character first introduced as Clayface, was not shape-shifting clay monster that fans know of today. The first and current Clayface, Basil Karlo - inspired by horror film actors Boris Karloff and Basil Rathbone - was an actor who wore the costume of one of the characters he played, Clayface, in order to to kill other actors for not getting a part in movie. He wouldn't become a shape-shifter until the Post-Crisis continuity of Batman, when he injects himself with the DNA of other Clayfaces, the shape-shifting Preston Payne and Sandra Fuller (Lady Clayface). It's all very complicated, as comic books usually are.
5 The Penguin
A classic Batman villain who at one point was, debatably, at the same level of importance as the Joker. Oswald Cobblepot was a genius thief, who first appeared in Detective Comics #58 and repeatedly came to cross paths with the caped crusader. At some point in the comics, Batman acknowledges the Penguin as being no matter that him, a feat not many villains have accomplished. This is also backed by the fact that he is one of the select-few Batman villains that is sane, and he's one of the first two Batman rogues to team-up against the Caped Crusader; the other being the Joker. Despite his size and fancy outfit, he is considered one of Batman's deadliest foes.
4 Harvey Dent/Two-Face
Harvey Dent's first appearances are, weird to say the least. He first appeared as Harvey Apollo Kent in Detective Comics #66, before renamed Harvey Dent in later issues. At the time, he was considered the most serious of Batman's enemies, since he became a criminal after acid was thrown at his face, where he went insane. But what made him notable was that he didn't have a duo-persona, instead he would simply commit acts of crime or charity based on the toss of his iconic coin. He was actually cured of his disfigured face in his third appearance in 1943, but later appeared disfigured again in later issues. Whether this was a retcon for the Post-Crisis continuity or not was never truly stated.
3 The Riddler
The flamboyant Batman villain made his first appearance in Detective Comics #140, and is the eighth villain to return in later titles and continue to appear in the Post-Crisis timeline. He's a genius who continually tried to prove his intelligence, using his obsession with puzzles and riddles as a way of getting the better of the Dark Knight.
He mainly used this as a way to distract Batman from a hidden scheme of his, but more often simply tried to prove his superior genius. His most common costume was the use of a domino mask, despite being associated with the green-leotard covered in question mans he first used during his first appearance.
2 The Mad Hatter
The Mad Hatter's creators purposely made him to be a character who just really likes hats. Deranged and obsessive, he made his appearance in Batman #49, as a short-sized but genius man trying to steal a trophy. He is foiled by Batman, and not seen again until over a decade later during the Post-Crisis Silver Age. It was only then that he became a regular Batman rogue. His whole M.O. is really that he likes big hats, talks in rhymes, and is obsessed with the Hatter character from Alice in Wonderland.
1 Deadshot
Most modern fans might not know this, but Deadshot first appeared as a Batman villain. He was originally an assassin who tried to replace Batman as Gotham's protector, but was evidently defeated by the Dark Knight. During his first appearance in Batman #59, he wore a suit and top hat, a gun-belt to holster his pistols, and a domino mask to cover his identity. The character wouldn't appear in his famous red costume until Detectives Comics #474, where he acquires his famous monocle from none other than the Penguin.