Clint Eastwood was supposed to play this classic villain in Batman 1966
It was almost certain... and then the series got cancelled.
One of the best parts of the 1966 Batman series with Adam West is undeniably the rogues gallery of villains. Cesar Romero as The Joker (complete with painted-over mustache), Burgess Meredith as The Penguin, Julie Newmar and Eartha Kitt's double duty as Catwoman — all of them defined these classic characters for a whole generation. Even smaller, less-seen villains are still memorable over fifty years later. We're especially fond of Vincent Price as Egghead.
However, there's one notable villain that we didn't see that nearly joined the ranks of these greats.
Harvey Dent, better known as Two-Face, has been one of Batman's longest-running adversaries. First appearing in 1942, Dent was originally a Gotham City District Attorney who went insane after his face was damaged when a mob boss threw chemicals on him during a trial. Over the years, Two-Face has been brought to life by such actors as Tommy Lee Jones, Billy Dee Williams, and even Captain Kirk himself, William Shatner!
While Two-Face didn't make an appearance on Batman 1966, he was on his way. According to the 60s Batman Wiki, show creators considered Two-Face early on, but thought that he was too gruesome for the more campy, family-friendly tone of the show. However, as ratings began to drop later in the show's run, they thought about pulling him back out. This Two-Face would be a TV reporter, not an attorney, whose face is damaged from an explosion involving studio lights.
Clint Eastwood, fresh off his success from The Good, The Bad, and The Ugly was reportedly in talks to play the iconic character. Sci-fi author Harlan Ellison wrote a story treatment. Martin Grams, a pop culture author who has written over thirty books on shows like The Twilight Zone and The Green Hornet, says that he's seen production papers that say Two-Face was "almost a certainty" with "Clint Eastwood slated for the role".
Alas, the show was cancelled before this could happen. However, in 2015, DC Comics put out a one-shot comic titled Batman '66: The Lost Episode that used Ellison's original story treatment. So you may never be able to see Eastwood as Two-Face, but you can revisit the story in print and think about what might have been.