Azrael-As-Batman: The old Batman was created for older times.
Over the course of a long-running series, something happens to the main character. He loses his powers, makes a Heroic Sacrifice, or gets Older and Wiser and decides to retire. Sometimes they Dropped a Bridge on Him, or Put Him On A Bus. In a word, he's gone. But the story still goes on! His role is taken by a Suspiciously Similar Substitute, but one with a very different characterization. He's how the original hero would be if he were a Jerkass, Anti-Hero or (most commonly) '90s Anti-Hero.
Depending on how he's portrayed, he may be a Replacement Scrappy (especially if the original character were good on his/her own and the fans already like him/her) or a refreshing change (often happens if the fans are tired of having to look at the same hero over and over again). Sometimes the substitute may even be liked more than the original.
When the substitute is bad enough, there'll be often a storyline where the original hero is back and will have to fight the substitute for the position and wins. The substitute is then reduced to a villain (either minor or major) or just a minor hero. Alternatively, said substitute may be Rescued from the Scrappy Heap by giving them a Character Development and/or (when said substitute took the original's name) a name change.
This happened a lot during The Dark Age of Comic Books. Back then, it was common to presumptuously expect readers to like the new character, but writers have gotten savvier since then. Now, the Darker and Edgier version of the hero is commonly portrayed as a villain or a psychopath (or, sometimes, be redeemed), as the '90s Anti-Hero archetype has grown less popular over time. Some heroes were put through this in order to show why a hero shouldn't become Darker and Edgier as a subtle Take That! to the fandom. For example, Super Patriot replaced Captain America temporarily in the 1980's to show that the Cap'n wasn't the jingoistic, nationalistic unthinking supporter of the United States government some fans thought he was or wanted him to be.
- Happened to Astro Boy of all people in a one-shot gag manga Osamu Tezuka did as a nostalgia piece for Bungei Shunju, a popular men's magazine of the day. After Astro's apparent death in the final episode of the first TV series the ministry of science was ordered to create a replacement, but since they tried to make him more humanlike than the original he turned out to be a selfish, greedy, shiftless sex maniac.
- Since JoJo's Bizarre Adventure changes protagonists every part, this was bound to happen.
- Part 2: The polite and academic Jonathan Joestar is replaced with the streetwise and pragmatic Joseph Joestar.
- Part 3: The goofy and cheerful Joseph Joestar is replaced with the emotionally distant and serious Jotaro Kujo.
- Part 4: Basically the reverse happens: the emotionally distant and serious Jotaro Kujo is replaced with the goofy and cheerful Josuke Higashikata.
- Part 5: The kind-hearted Josuke Higashikata is replaced with the ruthless Giorno Giovanna.
- When Mazinger Z ended and Great Mazinger started, Hot-Blooded, happy go lucky, self-styled ally of justice Kouji Kabuto lost his main character spot to the ever frowning, warrior-first-hero-second (but still Hot-Blooded, we are talking giant robots here) Tetsuya Tsurugi. Needless to say there was a lot more angst this time around.
- In the Batman manga, the Hangman deliberately tries to do this to Batman, but Jumps Off The Slippery Slope right at the beginning by persuading a mentally-disabled man to commit a robbery and then killing him, to establish his vigilante credentials.
- The Gundam franchise has of course run the gamut of protagonists over its nearly 40-year history, but probably the biggest example of this is Mikazuki Augus, protagonist of Mobile Suit Gundam: Iron-Blooded Orphans. The heroes of the last few Gundam series before him (particularly Kira Yamato, Setsuna F. Seiei and Kio Asuno) were All Loving Heroes and Messianic Archetypes who deliberately avoided killing even enemy combatants. In contrast, Mika is a Combat Pragmatist Child Soldier who doesn't spare his opponents a second thought; if you attack him or his "family", he's going to kill you, and God help you if you actually hurt someone he cares about. He also contrasts with most other Gundam protagonists by not being a Warrior Therapist, and even shutting down opponents who try the same by telling them "You Talk Too Much", or just straight up killing them mid-sentence. His character is actually quite divisive among the fandom, with some detractors even claiming that his cold-blooded, merciless nature makes him a straight-up Villain Protagonist.
- Buffy the Vampire Slayer: When one Slayer dies another girl is called forward to take her place. Well Buffy did die and despite being revived is replaced by Kendra, a Knight Templar whose sole focus is on hunting and killing vampires regardless of who they are. When she died she was replaced by Faith, very much an Anti-Hero before, during and after her FaceHeel Turn. Not a typical example, since Buffy was only dead for a few minutes at most; so she continued being the main character and maintained the role as the main slayer. With Faith as the "active" slayer, if she died, a new slayer would have taken her place, but Buffy's later (temporary) death did not have any effect.
- Angel also did this with Spike, to comedic effect. Where Angel would pound rapists into the pavement and recieve a smooch as reward (to Spike's vocal disgust), "Blondie Bear" just chides the girls for stupidly walking home at night and alone.
- Keppler, the Temporary Substitute for CSI's Gil Grissom. He was prone to bending the rules a lot more than Grissom, and nearly got the whole team in trouble with his "reverse forensics" plan to nail a criminal they couldn't otherwise touch.
- At the beginning of season five of Boardwalk Empire, Nucky Thomson has replaced his bodyguard Eddie Kessler, who committed suicide when being blackmailed by the FBI. Kessler was affable, decent, but determined and capable in a fight — by no means a hero, but one of the nicest characters in the setting, and fast becoming a Morality Pet for Nucky. The replacement is silent, menacing, and viciously brutal in a fight — even slicing the ear off a dead attacker and keeping it in his suit pocket. The implication is that Nucky hates that he got personally attached to Kessler only to lose him, and has hired a bloodthirsty stoic he won't mistake for a friend.
Senator: Doesn't say much, does he?
Nucky: That's what I like about him.
- It has happened in Doctor Who four times so far.
- When the mild-mannered Fifth Doctor died and regenerated into the Sixth, who was frequently a Jerkass, controversially violent, and started his life by trying to kill his own companion in a bout of post-regenerative psychosis. (Not that Five didn't get up to some violent acts himself, but he seemed much more conflicted about it.)
- The Eighth Doctor sat on the sidelines during the Time War, a major interstellar conflict set in-between the classic series and the revamp. Upon learning that an seemingly fatal incident he was involved in actually was fatal, meaning that he was already dead, he chose to drink an elixir that was specifically formulated to give Time Lords more-than-usual conscious control over the nature of their next self, becoming the "War Doctor", played by John Hurt, who was specifically crafted by his former self to be a person who would do anything necessary to end the war. What the War Doctor eventually did led to his subsequent selves refusing to even consider him deserving of being called "the Doctor", to the point that it's strongly implied that he is the one thing in the universe that Eleven is most frightened of.
This is lampooned in the Inspector Spacetime "series", in which the Inspector was very briefly played by an A-list actor and bummed around as a dirty cop.
- They did it again when the Eleventh Doctor regenerates into the far more abrasive and openly ruthless Twelve, with his main character arc for his first season revolving around whether he still counts as a "good man", which he himself doubts.
- And again, revealed gradually with Thirteen, as while Twelve character developmented into a much softer version of himself, he also had a buttload of trauma that unlike the other Doctors he had no time to process, plus wanted to die for real, so Thirteen represses everything, shuts herself off and her simmering rage comes out in a sadistic Grin of Audacity at the villains in season 11, and outright yelling at her companions in season 12.
- To a lesser extent, there was also the transition from Three (a well-dressed, gentlemanly iteration who was something of a Jerk with a Heart of Gold but was generally heroic) to Four (a manipulative, egotistical, vaguely loopy Manchild with a much more casual attitude towards death, who dressed like a Rummage Sale Reject to conceal a mind like a steel trap, albeit one with something of a wonky spring).
- Johnny Lawrence in Cobra Kai is like Miyagi in that he mentors young people... but he's also a Jerk with a Heart of Gold.
- The introduction of K' in The King of Fighters '99, blatant attempt at Darker and Edgier, had a very mixed reception. Unlike most examples however, he received enough Character Development to save him from the heap, and is now a fan favourite. Then SNK went even further down the line with Villain Protagonist Ash Crimson in the next arc. The reception was even more mixed.
- The Legend of Dragoon has Shana get benched and lose her power as a Dragoon. Her successor is Miranda, a Warrior Princess with a penchant for punching people.
- Plutia in Hyperdimension Neptunia Victory is considered a Suspiciously Similar Substitute for Compa from earlier games, as both are The Ditz and Combat Medic. Unlike Compa, however, Plutia is less heroic and more like a Token Evil Teammate, scaremonger and Villain Protagonist, especially as Iris Heart; she pretty much spends most of her time scaring friend and foe alike. Much like Ash Crimson above, the reception was mixed, even in the West where she's generally better received.
- Umineko: When They Cry:
- Villainous example. Beatrice gave her title to Eva's hidden personality. When Eva-Beatrice was acting like a monster all-time, Beato get a few Pet the Dog moments, and got to make a Heroic Sacrifice, after realizing her mistakes. Then it's revealed it was all a clever Batman Gambit she put in order to make Battler admit she's a witch.
- EP 5 replaces Battler himself for Furudo Erika. It's played with irony considering the second is more or less an aspect of the Big Bad and Battler is not incapacitated and actively fighting the against change.