Great heroes are defined by the villains they face, and no group of evil-doers, murderers, criminals and psychopaths are greater than those stalking Gotham City. From murderous clowns, to cerebral assassins, to brutish monsters, Batman has a literal murderer's row of foes that constantly test his crime fighting acumen. Today CBR News prevents the first of a two-part series on the DC Comics villains who have given Batman his greatest challenges; the nemeses who have helped forge the legend of the Dark Knight for the past 75 years -- and hopefully 75 more to come!

While many can likely guess the top foe on this list, we think there will be plenty of twists and turns along the way. Secondly, we want to give love and respect to Selena Kyle, AKA Catwoman, and acknowledge her contribution to the world of Batman. For the purposes of this article, we are forced to consider Catwoman an ally (albeit, at times, reluctantly), not a sworn blood enemy. With that in mind, sit back and enjoy #20-11 of the greatest Dark Knight villains of all-time, and be sure to check back tomorrow for the Top 10!

20. Mr. Zzasz

First appearance "Batman: Shadow of the Bat" #1 (1992)

Created by Alan Grant and Norm Breyfogle

Mr. Zzasz is one of Batman's most disturbing foes in that he is simply a lunatic with a knife, a desire for blood and no moral consciousness whatsoever. Zzasz's trademark is carving a tally mark into his own body after each kill, a character perversion that separates him from the pack of other literary serial killers. He does not kill for profit or power -- only for fun. Like Henry Lee Lucas or Richard Speck, Zzasz is a modern nightmare, a killer lurking in the shadows with an insatiable need to feed his own dark appetites. Worse of all, Zzasz is almost a mental match for Batman. Gotham's dark tally man is a killer with a brilliant mind ready to carve the city's denizens into pieces to suit his own perverted desires. There are some terrifying monsters on this list, but Zzasz may just be the most monstrously human of them all.

19. King Tut

First appearance (television)"The Curse of Tut" 1966

First appearance (comic) "Batman Confidential" #26

Created by Christina Weir, Nunzio DeFilippis and Jose Luis García-López

Tut is one of only a handful of characters in superhero history to be created on television and later make the jump to comics -- and, in Tut's case, it happened decades later. When Tut first appeared in the "Batman" TV show in 1966, actor Victor Buono's performance was so unforgettable it seemed like the character had been established in the comics for decades. Thanks to Buono's portrayal of a brain-damaged (and very Caucasian) history professor who got bonked on the head and believed himself to be the legendary King Tut, the faux Egyptian ne'er do well became an accepted part of the Bat mythos. Many non-comics fans were surprised to learn Tut had never tangled with Batman in the comics and was created especially for the show, at least until 2009, when DC introduced a very different King Tut to the comics 43 years after Buono camped his way into becoming a pop culture legend. This inclusion in the world of comics speaks to Tut's resonance and is the main reason he makes this villainous Hall of Fame while characters like Egghead and Louie the Lilac are left in the dust.

18. Ventriloquist

First appearance "Detective Comics" #583 (1988)

Created by Alan Grant, John Wagner and Norm Breyfogle

Arnold Wesker is truly one of Batman's best foes conceptually and visually, a small and mousy man who channels his evil heart through an Edward J. Robinson like ventriloquist dummy named Scarface. The Ventriloquist is one of Gotham's most ruthless crime bosses, and despite his comedic appearance, is also one of Batman's most cunning and enduring foes. The Ventriloquist is such a high concept villain that it's only a matter of time before some filmmaker or showrunner approrpriates him for use in another medium and makes him a househould name. The Ventriloquist and Scarface will fill anyone full of lead that dares laugh at the tommy gun-wielding puppet. Over the past few years, there have been several new villains wielding the Ventriloquist name, including a femme fatale and her puppet Ferdie who currently hold the Ventriloquist moniler in the New 52, but it was Wesker and Scarface that started it all.

17. Killer Croc

First Appearance "Batman" #357 (1983)

Created by Gerry Conway, Gene Colan and Curt Swan

While a villain created by the legendary Gene Colan, Curt Swan and Gerry Conway seemingly deserves a place on any list, add that pedigree to the fact the Waylon Jones is arguably one of Batman's most physically fearsome foes and you have a villain for the ages. The only drawback for Killer Croc is that his intellect doesn't match his physical prowess. What Croc lacks in brains, he more than makes up for in brawn. An old school goon, Killer Croc is a remnant of the days of Dick Tracy, a deformed, physically shocking rogue who feeds his greed with the same ravenous intensity his swamp dwelling namesake feeds its belly with. Croc has had many physical iterations over the years, from a bestial man with a hideous skin disease that resembles a crocodile, to a literal human/croc hybrid; Killer Croc has always been the nightmare dwelling in Gotham sewers, a figurative dragon in Gotham's underbelly waiting to devour anyone foolish enough to venture into his domain. Croc is a great character with roots firmly entrenched in classic horror, but he has also been played for laughs over the decades. Who can forget the "I threw a rock at him" gem from "Batman: The Animated Series?" Whether played for laughs or as a visceral threat, Croc remains one of Batman's greatest foes.

16. Mad Hatter

First appearance "Batman" #49 (1948)

Created by Bill Finger and Bob Kane

The greatest addition to Batman's rogues gallery from the waning days of the Golden Age, the Mad Hatter is the dark reflection of a beloved children's character, a villain who makes the sacred stories of youth into something twisted and profane. In the innocent Golden Age, Jervis Tetch was a hat-obsessed petty crook who used mind control technology to illegally obtain rare hats for his beloved collection, but in the more modern era, Tetch is a crazed puppeteer, often dangerously obsessed with controlling women he would often cast in the role of Alice in his own twisted version of Lewis Carroll's classic. The modern Hatter is a nightmarish figure that twists innocent fairy tales to perfectly fit Batman's dark world. Actor David Wayne brought the villain to iconic status with his portrayal of the Hatter in the '60s "Batman" TV show.

15. Man-Bat

First appearance "Detective Comics" #400 (1970)

Created by Frank Robbins and Neal Adams

Sometime hero, sometime cannibalistic monster, Kirk Langstrom invented a serum that would allow deaf people to develop bat-like sonar. This being comics, the serum transformed Langstrom into a giant bipedal bat who terrorized Gotham. Man-Bat is a special challenge for Batman because the Dark Knight wants to cure the monster rather than hurt him; not an easy thing to do when battling an eight-foot tall bat with steak knives for teeth and a serious hunger. Langstrom's formula has become just as fearsome a threat as he is. A number of characters including Langstrom's own wife have taken the serum and transformed themselves into serious threats to Batman and the DC Universe. The serum was also used by Talia Al Ghul to create a regiment of Man-bat ninja bodyguards. There is nothing not awesome about Man-Bat ninjas.

14. Clayface

First appearance "Detective Comics" #40 (1940)

Created by Bob Kane, Bill Finger and Sheldon Moldoff

There have been eight(!) different villains that have served the Clayface legacy since Basil Karlo first appeared in 1940. Karlo was a Lon Chaney-like figure driven insane when he learned one of his classic films would be remade without him. A master of disguise, Karlo attempted to sabotage the film until he was defeated by Batman. The next version of Clayface was a much more literal interpretation. Criminal Matt Hagan used a radioactive mud pool to turn his body into a mud-like mass that could change shape and form. The many villains that followed were a derivative of Hagan, except for Clayface III who looked like his face had melted and was in love with a wax mannequin (seriously). The current Clayface is a mash-up of Karlo with Hagan's powers and follows the visual established by "Batman: The Animated Series." Clayface is another monstrous rogue who tests both the wit and strength of Batman. When battling Clayface, Batman must use every ounce of his physical ability to stop the mountain of insane goo but the hero must also use his smarts to find and defeat a villain that can literally be anything.

13. Hugo Strange

First appearance "Detective Comics" #36 (1940)

Created by Bill Finger and Bob Kane

The antagonist in Batman's ninth appearance, Hugo Strange is the first recurring Bat foe and still remains Batman's most cerebral adversary. In his first appearance, Strange experimented on four escaped mental patients, transforming them into hulking, lobotomized zombies and tasked them with capturing Batman. In the dawning days of superhero comics, most villains robbed banks or sabotaged military bases, but Strange spent his evil days creating insane zombie ogres, upping the ante for the other Bat villains who followed. Not many villains have survived from the Batman's earliest days, but Strange is still with us, in cartoons, comics and video games as a featured and cognitively formidable villain that mentally challenges Batman wherever and whenever the not so good Doctor shows up.

12. Mr. Freeze

First appearance as Mr. Zero: "Batman" #121 (1959); as Mr. Freeze: "Detective Comics" #373 (1968)

Created by Bob Kane, David Wood and Sheldon Moldoff

Originally known as Mr. Zero, Victor Fries was one of Batman's first super-powered villains. When he first appeared, Mr. Zero was a gimmicky villain who was forced to wear a containment suit to keep his body beneath a certain temperature. This stone cold criminal used a cold gun to make life miserable for Gotham City. He appeared throughout the Silver Age, and while never gaining the cache of the Joker, he carved himself a niche as a persistent foe. Zero went from footnote to legend when the '60s "Batman" TV show changed the villain's name to Mr. Freeze and cast him as a major foe to Adam West and Burt Ward's paunchy crusaders. Freeze was ably played by three separate actors, each bringing their own nuances to the character.George Sanders, Otto Preminger and Eli Wallach each played Freeze in separate two-parters spread throughout the show's three-season run. While his TV and comic book appearances created a lengthy history for Mr. Freeze, it was Bruce Timm and Paul Dini that made him a legend in their 1992 Emmy Award-winning episode of "Batman: The Animated Series" entitled "Heart of Ice." In this episode, Freeze went from a gimmick laden villain to one fraught with nuanced tragedy. Dini and Timm added the element of Freeze's wife Nora, a beautiful woman stuck in a cryogenic sleep that Freeze would destroy all of Gotham to cure. Freeze has changed and endured throughout many different comic eras and remains one of Batman's most persistent and nuanced foes. The villain's legacy even survived Arnold Schwarzenegger's legendarily awful performance in 1997's much maligned "Batman and Robin."

11. Poison Ivy

First appearance "Batman" #181 (1966)

Created by Robert Kanigher and Sheldon Moldoff

The greatest villains are the heroes of their own stories, and environmental crusader Pamela Isley could have been one of the planet's great defenders had she chosen to channel her passion into more heroic channels. Instead, she is a contagious, twisted, fevered, environmental terrorist who values the well being of a rhododendron over the value of thousands of human lives. Poison Ivy means well -- in her own twisted way -- but like an uncontrollable force of nature, she leaves destruction and pain in her wake. An avatar for the fury of Mother Nature, Poison Ivy has been tempting and plaguing the heroes of Gotham since the '60s. In recent times, thanks to her uncharacteristic loyalty and friendship with Harley Quinn, Ivy has been cast as somewhat of an anti-hero, but her unpredictable nature makes her a constant threat to any but her leafy, flowery friends. She might be Batman's most beautiful villain, but this rose has thorns and a heart of pure poison.

Check back tomorrow for the Top 10!