Heroes who gave up being heroes because of what catastrophe had happened, wanting to live a normal life, or simply fulfilling their duty and/or choosing their own ways to move forward. Some of them might come back.

Here are a few examples of Retired Heroes:

1. Agent K: After he and his partner Agent J have defeated Edgar The Bug, they return to MIB Headquarters with Weaver. J thought he was going to neuralyze Laurel, instead, K grabs his neuralyzer and explains that she isn't going to get neuralyzed, when it's K himself. K tells J that he hasn't been training a partner, when in fact he has been training a replacement. K explains to him how to properly use the neuralyzer he hands it to J. K says "See you around.," and smiles. J replies "No you won't.", and neuralyzes him. After K retires, it is explained that he was in a coma for all of those years, and returned to his wife, he left behind in 1961. In Men In Black II, when the world is at stake again from Serleena, they have to bring him back to MIB Headquarters and restore all of his memories.
2. Brian O'Conner: He agrees to help Dominic Toretto and his crew do one last job before he can spend some time with his family in Los Angeles.
3. Peter Parker: He struggles to manage both of his personal life and his duties as Spider-Man, somehow he lost all of his powers and threw away his suit in a bin. He returns to his normal life and tries to fix things up with his love interest Mary Jane Watson. When Doctor Octopus kidnaps Mary Jane, his powers have returned also steals back his suit from the Daily Bugle and goes after him.
4. David (Pleasantville ): David, after making Pleasantville a more fun and realistic place, left Pleasantville, and focused on his normal life.