I have compiled a list of characters that I think fit the bill of Extreme Makeover. Unless you're a geek, chances are you'll not likely think that they are in fact the very same character at all.
We start off with the Avengers:
Captain America (Steve Rogers). On 1 of his missions, back in the 70s, he was required to disguise himself as the Nomad. Then on another occasion in the 80s, he had to take on the persona of The Captain due to conflicting ideologies of the govt big-wigs.
Then in Dark Reign, when Norman Osborn (Green Goblin) took over as Head of SHIELD, and eventually outed as a villain, Capt America took over the reigns as Director of SHIELD (which is the version we saw in the MCU)
Fans of the Marvel Cinematic Universe (MCU) may not be familiar with the classic Thor design shown here. However, before the current version that everyone knows, Thor had a few Extreme Makeovers before such as the time when he was literally turned into a frog (!!!) by a spell. Then, a curse caused all his battle injuries to not heal and he relied on an armor to keep his body from falling apart.
I of course didn't forget about one of the MCU fan faves - Iron Man. All of his other older armors have been presented in a different post - HERE.
The Vision, who started off as a villain (created by Ultron, as fans of both the MCU and books would know) but would eventually became one of my favorite Avengers of ALL TIME. Here are some of his Extreme Makeovers.
Ant-Man (Hank Pym) was in fact one of the founding members of the Avengers along with Thor, Iron Man, Hulk & the Wasp (Janet Van Dyne)
While this is not what the MCU fans would be familiar with, in the comic book world he was and had many changes to not only his costume, powers but also the names, from Giant Man to Goliath and Yellow Jacket.
Of course, no discussion of Hank Pym would be complete without the Wasp (Janet Van Dyne), who is the other Avengers founding member. She is well known for her costume changes long before it became cool to do so.
Wonder Man (Simon Williams), who started off as an enemy to the team (this seems to be SOP for many Avengers) but eventually became a key member of many incarnations of the team.
The Original Captain Marvel (Mar-Vell), a Kree warrior. A key player in the fight against Thanos (Yes, THAT Thanos).
Not to be confused with his son Genis-Vell (who took on the Captain Marvel mantle after his dad died from cancer in the landmark Marvel GN#1 - Death of Captain Marvel)
Before the introduction of Genis-Vell, Marvel tried to fill the shoes with Monica Rambeau (introduced in Amazing Spider-Man Annual 16), before changing her name to Photon and then later to Pulsar (yeah, I also get confused by so many name changes), the leader of the team called Nextwave, Agents of HATE (Highest Anti-Terrorism Effort)
Also not to be confused with the current Captain Marvel, a title held by Carol Danvers who used to be known as Ms Marvel. She started off as a sort of side-kick/female version of Capt Marvel (a la She-Hulk, Spider-Woman, etc) but eventually taking on the role originally filled by the now deceased Captain Mar-Vell. At one point in time, she even turned into a cosmic powered being called Binary (introduced in Uncanny X-Men 164). Speculations are rife that this will be the version of Captain Marvel we will see in the next Avengers Movie.
And of course we have the HULK. Many already know that when the HULK first appeared in comics, he was grey. Eventually, he became the jade giant we all know and love.
Then at one point, they gave him back his intelligence but slightly weaker (because he didn't really get mad that easily anymore), but he wasn't a really nice guy called Mr Fixit. In the early 90s, there was a great HULK story called Future Imperfect where we were introduced to the Maestro - an alternate future version of the HULK who is a villainous despot.
The most recent Extreme Makeover the HULK had was the Planet Hulk look (which I think looks pretty darn cool for a statue).