As mentioned elsewhere the Big Two comic book companies have a stable of characters culled from decades of trial and error with proven staying power but sometimes they want to launch a new character for various reasons. New characters tend to fail due to a combination of Sturgeon's Law and fandom's attachment to the existing vetted characters. Legacy Characters do inject fresh blood into a title sometimes but they only revitalize the existing franchises rather than creating new ones. The solution is the Legacy Launch. It works something like this.
- Trope Man aka Bob retires or is killed off.
- David steps up as the new Trope Man.
- After a while, a fandom has developed for David, and Bob returns.
- David graciously abdicates Trope Man back to the original.
- David becomes The Deadpan Snarker.
- Iron Man Tony Stark is replaced by James Rhodes. When Stark returns to the role, Rhodey becomes War Machine, which is basically Iron Man with More Dakka and a military background.
- Thor was bonded to another mortal temporarily. When Thor was separated and banished, the mortal, having been valorous and physically dependent on the joining was given his own powers to become Thunderstrike.
- Captain America was forced to surrender his identity to the US Government which was then given to John Walker. When Steve got it back, John became US Agent.
- John Henry Irons was introduced as a potential Legacy Character for Superman but the plan all along was for Superman to return and Irons continued on as "Steel" with only the S-Shield missing (though he was already very different from Superman.)
- Jean-Paul Valley was briefly Batman but went crazy forcing Bruce to return to the mantle. After rehabilitating, Valley became Azrael.
- Hank Pym has inverted this, having created a number of identities for himself, Giant Man, Goliath, Ant Man, and Yellow Jacket because he was never quite happy with them but has allowed other characters to use these identities (including Hawkeye who already had his own identity.)
Hello, Unknown Troper. You'll need to get known to lend a hand here.