In TV, it’s called The Other Darrin. See, back when Bewitched first hit the airwaves, the character of mild-mannered husband Darrin was played by a guy named Dick York. When York became sick after a couple seasons (presumably from illness, not from all the fetching nose wiggling), they swapped him out for a guy named Dick Sargent. Bewitched ran another three years, Dick York for another 20, giving him the last laugh.

Same character, blatantly different actor. It happens all the time. The internet is a little loose with this definition. They’ll count the fact that there have been four Batmans, or three Jack Ryans, or 403 different James Bonds. But usually those types of movies stand as individual films, with only incidental continuity needed between one film and the next.

On the other hand, occasionally you get movies that are obviously part of a larger story. When an actor bows out (or dies, or makes too many unreasonable demands), that’s when the craziness really heats up.

Here are my favorites.

Crazy Old Wizards

Harry Potter was originally planned as a 7-book series, and since one of the primary characters is a really old dude, the producers of the first movie had to be holding their breath at the thought of casting 973-year-old Richard Harris in the role of Hogwarts Headmaster Albus Dumbledore.

Harry Potter and the Sorceror’s Stone went off with out a hitch, was a massive success, and Harris was signed for the sequel, Harry Potter and the Chamber of Secrets. It would turn out to be his last film.

Knowing that they still had at least five more movies to go – more if they could saw a few of them in half – the producers turned to British actor Michael Gambon to replace Harris. Gambon was a high school junior at the time, and they buried him in a mountain of old age make-up and goat fur to disguise the transition. Gambon, who 5 movies later is now 70, should make it through the end of the last Potter film.

Superhero Sidekicks

Even though I just said that casting switcheroos in superhero movies don’t really bother me, it’s just weird when the hero remains the same but the people around him are different. It’s happened twice in recent memory.

Terrence Howard played the long suffering Jim Rhodes character in the period romantic drama Iron Man, which surprisingly grossed $24 billion worldwide, one of the leading indicators that there will be a sequel.

When it came to film Iron Man 2: Back in the Habit, suddenly there was a falling out. The producers heard that Howard didn’t like them, then Howard said that he did like them, just not in that way, then the producers got snippy and said something mean to one of Howard’s friends, so then he prank called their mothers. Anyway, Howard wasn’t asked back.

Fortunately Terrence Howard is black, and so the producers hit upon the ingenious method of casting another black guy, apparently because they think we can’t tell the difference. Don Cheadle was brought on board, and he got to fly around in the Iron Man suit in the sequel rather than just stand by shaking his head, thereby twisting the dagger in Howard’s back just a little more.

Oh, and we all know the girlfriend role doesn’t matter in superhero movies, right? How else can you explain the character of Rachel Dawes, who began life in Batman Begins as the pretty form of Katie Holmes, but suddenly found herself in the sleepy-eyed, husky-voiced persona of Maggie Gyllenhaal for The Dark Knight? Maybe Katie had her hands full just trying to talk Tom down off the couch.

The Lambs Are Screaming

Jodie Foster won an Oscar for her portrayal of FBI super-agent Clarice Starling in the psycho-thriller The Silence of the Lambs, an accomplishment that sounds impressive, until you realize that pretty much every single person associated with Silence of the Lambs won at least one Oscar.

When it came time for the sequel, Hannibal, Foster took one look at the script and decided that there was too much man-eating pig stuff and not enough Mel-Gibson-talking-to-a-beaver-puppet. She politely declined and went on to further her directing career.

This left the door open for Julianne Moore, who like Jodie Foster, is a flaming redhead with many Oscars on her mantel. Okay, not really. But she did just fine with her Southern accent. Still, it had to be a little disheartening that for the third Hannibal Lector movie, she was replaced by Edward Norton. Admittedly, he was playing a completely different character, but still.

Back to the Casting Couch

The Back to the Future series has one of the most confusing plots of all time, especially when it comes to the casting.

The movie initially hired a guy named Eric Stolz to play the part of Marty McFly, and as unbelievable as this is, they shot most of the movie this way. But after viewing dailies in which Stolz seemed to have all the comic timing of Al Gore at a funeral, he was sacked, and teen heartthrob Michael J. Fox was brought in, necessitating a reshoot of virtually everything.

Melora Hardin, best known today as Jan on The Office, was actually cast as McFly’s girlfriend Jennifer Parker, but at a staggering, Amazonian height of 5’7”, she towered over the diminutive Fox. She was let go in favor of Claudia Wells.

When Back to the Future II rolled around, casting problems popped up again. Cripsin Glover, so excellent as Marty’s dad George McFly in the first movie, apparently demanded his own private country and a flight on the space shuttle. The producers balked and instead hired a look-alike, who would only appear in the background, as well as hanging upside down as “old George” in the scenes set in 2015.

The bigger problem turned out to be Jennifer Parker, who had a more substantial role in Part II. Claudia Wells was no longer available, due to an illness in the family. The producers searched high and low and finally decided on Adventurous Babysitter and Karate Kid girlfriend Elizabeth Shue.

In order to sell Shue as the new Jennifer, Part II opens with a shot-for-shot recreation of the ending of Part I, with Shue instead of Wells. It can be fun to watch these two movies back to back, since in Part II, the performances by Fox and Christopher Lloyd (Doc) seem to be parodies of themselves.

Sexy Logic

This last switch is my favorite, only because it seems so arbitrary. In Star Trek II: The Wrath of Khan, the character of Saavik is one of two major new characters that are not part of the original Enterprise crew (the other, of course, is Khan).

Saavik, played by future Cheers waitress Kirstie Alley, is a Vulcan Starfleet officer in training who finds herself aboard the Enterprise while it is under attack by genetic superhuman Khan. Throughout the movie, she comes to learn from Captain Kirk and even from Mr. Spock himself that Vulcan logic and Starfleet regulations must sometimes take a back seat to outwitting wrathful, bare-chested TV icons with a doomsday weapon built by Kirk’s son.

Star Trek II kicked off the only real “trilogy” of the Star Trek movies, and Saavik would appear in both Star Trek III The Search for Spock and Star Trek IV The Voyage Home. Kirstie Alley, however, would not.

Robin Curtis replaced Alley in the Search for Spock, and was again a major character. She spends most of the movie falling in love with Kirk’s son David as they explore the Genesis planet, which has resurrected her fallen mentor, Spock. The truly odd thing about this is that Robin Curtis does not look remotely like Kirstie Alley. Her performance, while appropriately Vulcanish, lacks the inner turmoil at work in Alley’s. Their appearance and performances are so dissimilar that when I saw Star Trek III in my youth, I did not even realize it was the same character.

By Star Trek IV, the Klingons had managed to kill off Kirk’s son, leaving Saavik heartbroken — or, as Robin Curtis plays her, bored.  Saavik makes a token appearance on the planet Vulcan, wishing Kirk and the crew a safe trip back to Earth, and promptly exits the series.