Sometimes someone at a publishing company decides that a veteran hero "needs" to be replaced by a successor. By "successor," I mean someone who will use the same superhero alias, and sometimes the same costume, but will be (or claim to be) a different person. The reasoning behind this move can vary in different circumstances. Sometimes the plan is to give the old guy the boot to make room for the new guy in a hurry; other times the old guy has already been dead for years anyway! (Or just hasn't been heard from in any significant way for a long, long time, even if theoretically he's still alive somewhere.)
From the perspective of the other characters living in the same universe as the "old guy" and the "new guy," there are many possible reasons why the "old guy's" superhero role might be vacant, awaiting a successor. He could have died. He could have been injured badly enough (physically and/or psychologically) that he’s no longer fit for active duty; not now and maybe not ever. He could have voluntarily retired, either because of advancing age or simply because he discovered there were other things he wanted to do with his life -- such as getting married and raising kids -- without being distracted by every supervillain to hit town. He could have been fired from his superhero identity -- if his costumed role was actually in the nature of a “job” which he performed for an employer. He could have somehow lost whatever special powers or equipment made his heroic career possible (although otherwise he might still be in excellent health by any “normal” standards). He could have simply gotten tired of his old costumed identity and created a new costume and alias that he intended to use from now on (and he might be very frank about this and make it clear to the world that he was still the same hero --with a new paint job). He could have faked his own death in order to have some privacy from now on. Or maybe he just disappeared a long time ago and, as a new story begins, nobody seems to know which of the above possibilities is closest to the truth!
Be that as it may, if we grant there is a vacancy to be filled, what sort of successor might we end up with? Here are the possible types that occurred to me!
10 Types of Superhero Successors
01. The Carefully Groomed Protégé
02. The Family Member
03. The Copycat
04. The All-New, All-Different Version
05. The Rookie Created Out of Thin Air
06. The New Employee
07. The Mandated Replacement
08. The After-The-Fact Retconned Replacement
09. The Impostor
10. The False Replacement
Note: I'm ignoring "reboots" where nobody even remembers that there was a "previous user" of a certain heroic name. For instance, some fans have made a case that the Post-COIE Superman was effectively a "new guy" invented to "replace" both the Golden Age (Earth-2) and the Silver Age (Earth-1) versions of "Superman," but since nobody around him in the DCU remembered any previous versions of "Superman" they could compare him to, he didn't come across as any sort of "successor" in context. He certainly didn't think of himself that way! :)
Also: It's clear that these types can sometimes overlap, with a particular "successor" or "replacement" character belonging in two or more of those categories at once!
01. The Carefully Groomed Protégé
“My mentor always figured this day might come. For years, he worked to teach me everything he knew so that I’d be ready when it was time to fill his shoes!”
Wally West made his debut as “Kid Flash” in 1959. At the time, his Aunt Iris was Barry Allen’s girlfriend. After they got married, Wally was entitled to call Barry his “Uncle Barry.” (I’m not clear on how often he did, though.)
In 1985, Barry Allen died during the events of “Crisis on Infinite Earths.” Wally West soon took over the role. He was probably about twenty years old at the time. (Dick Grayson, his contemporary, a fellow founder of the original Teen Titans, was stated to be “twenty” during the events of COIE.) If we buy the version of Wally’s origin story that was later offered by Mark Waid in the "Born to Run" story arc (a four-part flashback sequence in the "Flash" title in the early 90s), then Wally got his speedster powers at the tender age of ten. So from Wally’s perspective, he had been Kid Flash for about ten years before moving up to take over his mentor’s role; and from the perspective of veteran DC readers, he had actually been training for this moment for about 26 years!
Diehard fans of the Silver Age Flash naturally were unhappy about Barry’s sacrifice, but as far as I have heard, it was generally accepted that if you granted the assumption that someone was going to “inherit” the mantle of the Flash now that Barry was gone, then that “someone” obviously ought to be Wally. No one (to the best of my knowledge) ever made a convincing argument in the late 80s that some other character would have been a better and more deserving choice! No one denied that Barry would have approved of Wally’s decision to keep the Flash tradition alive, had Barry still been around to actually comment on it.
Of course, this approach requires many years of prep time to firmly establish the idea with your fan base that the Protégé is well-qualified to someday “inherit” his mentor’s mantle, whether temporarily or permanently. Dick Grayson, for instance, had occasionally impersonated Batman in the past, but the first time he, as a grown man, really tried to make that stick for much more than ten minutes at a stretch was in the “Prodigal” story arc around late 1994. Since the basic character concept of “Dick Grayson, Robin, Batman’s protégé” debuted in 1940, you can see he had been "building up to this" in a way for about 54 years before he really tried to carry out Batman’s normal duties himself, day after day, on a “regular” basis as part of ongoing continuity (as opposed to such “out-of-continuity” stunts as some stories from the Silver Age that were presented as Alfred’s fictional rendition of what he thought might someday happen after Bruce retired).
02. The Family Member
“It’s a proud family tradition, and I aim to keep it alive!”
As mentioned, Wally West was the nephew of Barry Allen’s wife. Connor Hawke was the natural son of Ollie Queen and took over as “Green Arrow,” continuing the same monthly title, after Ollie was blown to smithereens. Ted Knight, the original Golden Age Starman, had two sons, David and Jack, and both of them served as “Starman” at different times. Jean Grey has used the aliases "Marvel Girl" and "Phoenix" at various times, and Rachel Grey (daughter of an alternate-timeline version of Jean) has also used both of those aliases at one time or another!
This category can obviously overlap with Protégé; and it can also get a lot of approval from the fans, since it makes a certain amount of sense that a aging hero might want one of his own bloodline to take over the “family business” – or if he dies, it makes sense that his child or other relative might feel particularly motivated to pick up where the hero left off (whether or not they had ever agreed to this in advance).
Of course, some fans may get snippy if a “long-lost relative” gets retconned into the old hero’s family tree just in time to dress up like his father (or big brother, or whoever). The publisher may hope that this “hip new younger version” will be greeted with open arms. The fans may instead say, “You snot-nosed punk; we never heard of you until they threw you in our faces just now! What makes you so great?” (See #05, below, for more discussion of this problem.)