Christopher Nolan's The Dark Knight trilogy reinvented a host of villains from Batman's rogues gallery, and teased a whole lot more. After Batman and Robin, the Batman franchise was in trouble. The campiness of that ill-fated 1997 outing had put what appeared to be the final nail in the coffin for Warner Brothers' original run of films based on the DC comics hero. But in 2005, Nolan reintroduced audiences to the character with a fresh, grounded take on the Batman universe with Batman Begins. Almost single-handedly giving birth to Hollywood's recent love affair with the gritty-reboot, the film would prove successful enough to spawn two sequels.

Nolan's The Dark Knight in 2008 and The Dark Knight Rises in 2012 continued the director's quest to ground his Batman in a realistic world. Eschewing the more fantastical elements of the character's comic book history, Nolan populated his Gotham City with characters that brought real emotional weight to his story, extending this sensibility to the various villains he chose to include. The most recognizable and widely-praised of these was the Joker, brought to terrifyingly vivid life by Heath Ledger in The Dark Knight. Alongside this most iconic of Batman foes, The Dark Knight trilogy also introduced original takes on such legendary villains as Two-Face, Bane, and Scarecrow.

Related: Why Scarecrow Is The Only Batman Villain In All 3 Dark Knight Trilogy Movies

Matt Reeves' The Batman will switch things up when it arrives in 2021, featuring Colin Farrell's Penguin as the main antagonist – a character Nolan steered clear of during his trilogy. But the Dark Knight films also set up several Batman villains that many viewers may have missed – hinting at their existence at various points throughout the three-film run. Some were barely teased, while others were featured in more than one scene throughout the trilogy. Here's all the villains Christopher Nolan's Dark Knight trilogy set up.

The Riddler

Coleman Reese in The Dark Knight

Alongside Joker, Two-Face, and Penguin, The Riddler is one of the most recognizable Batman villains - clashing with Bruce Wayne on an intellectual - as well as physical - level. Fans were naturally eager to see Riddler, aka Edward Nygma, show up in Nolan's trilogy. And as it turns out, they may well have gotten their wish - even if it was only a fleeting appearance. In The Dark Knight a resourceful Wayne Enterprises employee by the name of Coleman Reese uncovers Bruce Wayne' secret identity. Reese attempts to use the information to blackmail Morgan Freeman's Lucius Fox in a memorable scene that sees Fox dismiss the threat with his own ingenious logic. But it's possible this scene reveals more than Fox's penchant for dealing with threats of extortion.

Fox continuously refers to Coleman as “Mr. Reese,” which when said aloud sounds close to the word “mysteries”. In the comics, and the 1995 movie Batman Forever, Riddler's real name - E. Nygma - is actually a pun on the word “enigma”. Nygma is also a Wayne Enterprises employee who discovers his employer is Batman. Could Mr. Reese be Nolan's take on Riddler? It seems unlikely the director intended to develop Coleman Reese and have him actually become the Riddler. The character's story arc is relatively short, and this moment in the plot appears, if anything, to have been more of a tip of the hat to one of Batman's greatest villains, rather than a serious attempt to establish him in the trilogy. For now it remains unconfirmed, with only Nolan himself capable of solving the riddle. But with Paul Dano set to play The Riddler in next year's The Batman, fans may finally get the definitive Riddler performance they've been pining for.

Related: The Dark Knight: How Much Of Joker's Story Was Planned With Batman Begins

Clayface

Less high profile but with a solid foundation in Batman history, Clayface was also alluded to in Nolan's trilogy - indirectly, that is. First appearing in Detective Comics #40, Clayface has become a mainstay of Batman's rogues gallery, even if he never ascended to the villainous heights of Joker or Two-Face. And it seems Nolan decided to include a brief but unmistakable nod to the shapeshifting supervillain in The Dark Knight Rises.

What makes this subtle nod all the more intriguing is Nolan's decision to reference Batman: The Animated Series. In the celebrated cartoon run, Clayface is given a new origin story involving Roland Daggett - the CEO of a company that makes a face cream named Renuyu. He enlists the help of actor Matt Hagen to test the cream, eventually forcing Hagen into increasingly dangerous tests that result in him consuming toxic chemicals, transforming him into the villain Clayface.

While a shapeshifting villain would have undermined the gritty realism of Nolan's Batman universe, that didn't stop the director including his own version of Daggett in The Dark Knight Rises. In the film, Ben Mendelsohn takes on the role of Daggett, whose first name in the Nolan-verse is John. Daggett is the CEO of construction company Daggett Industries and is a direct rival to Bruce Wayne. Aside from using Bane to try to undermine Bruce's business interests, Daggett has a fairly limited story arc that includes no mention of Clayface himself. But the Daggett name was an unmistakable allusion to Batman: The Animated Series.

Related: The Dark Knight Rises Had Two Awesome Batman 66 Easter Eggs

Victor Zsasz

Tim Booth as Victor Zsasz in Batman Begins

Fans of the Batman comics and Arkham games will be familiar with Victor Zsasz. One of the Dark Knight's more debased foes, Zsasz was a serial killer who would carve tally marks on his skin for every one of his victims. The depraved villain first appeared in the 1992 Shadow Of The Bat run of comics and has cropped up in Batman-related media ever since, most recently appearing as a minion of Ewan McGregor's Black Mask in Birds Of Prey.

But long before Margot Robbie would face off against this relatively obscure Batman villain, Christopher Nolan made sure to include him in his first film in the Dark Knight trilogy. Batman Begins features Zsasz as a vicious former mob enforcer who Dr. Crane (Cillian Murphy) has transferred to Arkham Asylum from his prison cell. Later in the film, Katie Holmes' Rachel Dawes faces down Zsasz following his escape from the asylum, before Batman arrives to dispense with the deranged killer.

Although Zsasz has no lines in the film, his character is one of the most fully-realized of all the villains on this list. After being mentioned by Rachel early on in the film, Zsasz can be seen escaping from his cell at Arkham Asylum, just as one of his self-inflicted tally mark scars becomes visible. Portrayed by actor Tim Booth in Begins, Victor Zsasz wouldn't show up again in the trilogy, and certainly wouldn't have a storyline quite as elaborate as the other main Batman movie villains. But his appearance Begins was much more significant than many of the other minor references to great Batman villains, even if audiences at the time weren't aware of Zsasz's almost 15-year legacy in the comic books.

Related: How The Batman Could Set Up Arthur Fleck's Joker In Its Post-Credits

Killer Croc

Killer Croc

Bane and the League of Shadows provided suitably realistic antagonists for Nolan's final entry in the Dark Knight trilogy. But as with Clayface, Nolan couldn't help but include a characteristically wry nod to another one of Batman's more outlandish foes. In The Dark Knight Rises, following Commissioner Gordon's escape from Bane's sewer hideout, police officer John Blake (aka Robin) recounts how he tried to convince his colleagues of Bane's existence. He was met with a curt response: “They asked me if he saw any giant alligators.” Never one to resist an understated reference to an iconic piece of Batman history, Nolan here manages to weave a nod to Killer Croc into his humanized take on the Dark Knight.

In DC Comics, the supervillain Killer Croc is a murderous reptilian brute who first appeared in 1983's Detective Comics #524. In his original incarnation, the character was said to have been born with a medical condition that gave him a reptile-like appearance. In terms of his on-screen appearances, Croc showed up in Suicide Squad, but it would take some serious retcon work on the part of Nolan to fit the character into his trilogy without ruining the realistic tone he was striving for.

In this case, the “giant alligator” line from The Dark Knight Rises is clearly a tongue-in-cheek reference to the reptilian villain rather than a suggestion of his existence in the world of the trilogy. But as with all these examples, even the slight possibility of a wider array of villains existing in the Dark Knight trilogy is enough to gain fans' attention, and is yet another reason why the multi-layered series is as revered as it is.

Next: Dark Knight: The Actors Who Almost Played Batman In Nolan's Trilogy