Paul Bettany also portrayed Jarvis in the MCU.
Benedict Cumberbatch also portrayed Dormammu in the MCU.
Actors Who Have Played More Than One Comic Book Character
On an unrelated note, I somehow was able to remember "T'challa" faster than Black Panther.
Prior to 2008 there was a period of time when Marvel Comics was going through hard financial times and they sold off the movie rights to most of their most popular characters. The X-Men and Fantastic Four went to Fox. Spider-Man went to Sony. The Incredible Hulk, Blade, Ghost Rider, and the Punisher were sold off, as well. After the success of Fox's X-Men and Sony's Spider-Man movies, Marvel decided to try and produce their own movies, with the problem being they had sold off the rights to most of them.
Feige's plan succeeded brilliantly and since then many other studios have tried (and mostly failed) to copy it. But with one exception all of those popular Marvel characters I listed above still have their film rights owned by other studios. Marvel Studios might work on the films, or they may simply have the Marvel logo at the beginning, but they are not set in the MCU.
The Sony Spider-Man films Spider-Man, Spider-Man 2, Spider-Man 3, The Amazing Spider-Man, and TASM2 do NOT take place in the MCU... they are in their own alternate reality. Different universe/timeline and Marvel Studios had nothing to do with them.
It may get more confusing in the future as Sony is still producing their own Spider-verse films. The first one to come out since the deal with Marvel will be Venom. It's unclear if this will be considered part of the MCU or not.
Further in to the future, Disney is in the process of acquiring Fox, and once that deal goes through, since Disney owns Marvel, it's likely that the X-Men and Fantastic Four will also appear in the MCU.
Though knowing who played all of these roles will help you out if you take my quiz that I linked to above.
To the best of my knowledge the only actor to play multiple roles within the MCU is Benedict Cumberbatch, who portrayed both Doctor Strange and Dormammu, but I assume that was because the producers felt that nobody would recognize him as Dormammu.
Her character code names have been Captain Marvel, Photon, Pulsar, and Spectrum. Since you accept Quicksilver, a name Pietro never uses in the MCU, you may as well accept any of Monica's comic book code names, as well.
Also, it's starnge not to have "Woo" as a valid answer.
... it's odd to me, though, that you say you liked Guardians of the Galaxy so much and at the same time got turned off on the entire rest of the MCU because you saw some witty banter. Guardians probably has more goofing off during actions scenes than any other MCU film. so.. huh?
Anyway if you like RDJ... there's a full six hours of his character on screen if you watch all of these movies. Maybe they'll grow on you.
Maybe jmellor doesn't dislike witty banter during action scene but just one very specific trope? that of the action heroes who are perfectly cool under pressure even while the world explodes around them? I can understand that.
But then I was reflecting on this and the larger progressive arc of the MCU. And in a way, though they probably weren't planning this from the beginning it almost seems like they were if you watch all of these movies in series, it actually works to enhance the tension and payoff in Infinity War and Endgame. In Avengers, and especially Age of Ultron, I would agree the Avengers seem to completely outclass the antagonists in the film. Loki confronts Hulk and is immediately flattened. Ultron at one point attempts to take on all the Avengers, gets nearly obliterated, tries to quip and is punched into the horizon. Hydra's best plan of attack is to surrender.
Thanos comes along in Infinity War and in his first five minutes of screen time he has defeated Thor and in fact his entire race, killed the chief antagonist of the first Avengers film with his bare hands, and put the Hulk on his back. It's clear the stakes have been raised significantly, and you don't see any heroes in that movie acting as though this is a routine or insignificant threat. The events of the last two Avengers films would not have felt so big, nor the villain of those films as intimidating, if not for all the stories that came before building up to them. It was really masterfully done.
Or even if he had a cameo where he says the iconic line "You complete me." from the Jerry Maguire film. I know I would be cracking up in the theater!