Aldrich Killan from Iron Man 3 thanks being played by Guy Pearceis a far cry from jowly plain-faced scientist seen in Iron Man Extremis.
This isLoki in the Thor comics. This is◊ Tom Hiddleston as Loki in the movies. Good grief. There's a reason why he has so many fangirls. Coincidentally, the Norse god of mischief was described as "pleasing and handsome" (an alternate translation is "beautiful and comely," which is closer to our modern definition of a Pretty Boy) in the original myths. Marvel later came up with a younger version of Loki... who looks suspiciously like Tom Hiddleston.
In Doctor Strange, Karl Mordo is played by Chiwetel Ejiofor, a very handsome actor who has even been included in People Magazine's annual "Sexiest Man Alive" feature. This is in sharpcontrast to the comics, where Mordo (especially when drawn by Steve Ditko) was often depicted as an unappealing middle-aged man with a prominent widow's peak.
Homecoming also makes the Vulture younger and better looking. Michael Keaton may not be a spring chicken, but the comic version of the Vulture is usually depicted as a wrinkled old man with a large, bird-like nose and a scrawny physique.
In the comics, Helmut Zemo has to wear a mask to hide his charred, hideously disfigured face. In the above-mentioned Civil War, he's played by the handsome Daniel Brühl without any sort of mask or facial prosthetics. He begins wearing a mask in The Falcon and the Winter Soldier, and there's always the possibility his face could be burned in a future movie or TV show.
The Grandmaster of the comics is blue-skinned with a large, balding head. In Thor: Ragnarok he's played by launcher of a thousand "Daddy" memes Jeff Goldblum, with his natural skin color untouched (so as not to look too similar to his Earth Girls Are Easy character — also a blue extraterrestrial — according to the director) and silvery hair intact.
Much like the Hulk, Thanos isn’t really a looker in the comics due to being born with the Deviant Syndrome, and his mother tried to kill him as soon as she laid eyes on him. In most depictions, Thanos has unsettling features with Glowing Eyes of Doom and a Slasher Smile whereas in the MCU, thanks to Josh Brolin’s mocapping, Thanos has quite the rugged face with normal eyes.
In Black Widow (2021), Melina Vostokoff is played by the very beautiful Rachel Weisz, who notably lacks the Destro-esque metallic face of her comic version. Appropriate given she’s an ally of Black Widow, rather than a minor villain of Natasha in this continuity.
Spider-Man: No Way Home interestingly provides Adaptational Attractiveness to a character from another movie: Jamie Foxx's Max Dillon/Electro from The Amazing Spider-Man 2, who, as the Lizard puts it, originally had "bad teeth, glasses, and a combover" before turning into a blue-skinned Humanoid Abomination. Once he enters the MCU in No Way Home and reconstitutes his body, he's inexplicably transformed into a normal-looking (handsome, even) human with a sidecut and goatee, a healthier bronzed complexion, and actual muscle tone. His new body also lacks the imperfections of his original one, with Max now sporting better teeth, a full head of hair, and improved vision (thus eliminating the need for glasses). His new appearance is a factor in Electro wanting to stay on Earth-199999 rather than return to his home reality.
The film introduces Ghost, who is a plain-looking older man in the comics, and does a Gender Flip on the character so that she can be portrayed by Hannah John-Kamen as a beautiful young woman in the film.
Elihas Starr, known as Egghead in the comics, is still a bald scientist, but his head isn’t abnormally shaped to look like a literal egg.
In Thor: Love and Thunder, Gorr is a Downplayed example. The comic version of Gorr from Thor: God of Thunder was a hideous alien with a bulbous noseless face, fangs, Twi'lek-like head-tails, and a disheveled look. Here, he looks more human-like, is clad in a white robe, and is played by Mr. FanserviceChristian Bale... though he still has Scary Teeth, and the Necrosword's corruption has given him Supernatural Gold Eyes, Tainted Veins, and turned his gums, teeth, fingertips, and the area around his eyes pitch black.
Despite having a large head, M.O.D.O.K. is less hideous in Ant-Man and the Wasp: Quantumania compared to his appearance in the comics.
Deadpool is a very scarred character in the comic with (his appearances varying between the comics). His film counterpart portrayed by Ryan Reynolds is much less scarred than his comic book counterpart. Just like in the comics, his appearance is Played for Drama AND Played for Laughs with a lot of people commenting about his disturbing appearance in-universe.
Edwin Jarvis is slimmer and has a head full of hair, as opposed to the portly, balding Jarvis of the comics. His cameo in Avengers: Endgame also shows he aged very gracefully in 1970.
In the comics, Whitney Frost is the supervillainess Madame Masque, named because of the mask she wore to hide her face having a plane crash disfigured her. In the series, no such thing happened.
Harold Meachum in the comics was a crippled old man who lost his legs. Here, he is much younger and able-bodied as a result of becoming immortal by making a deal with the Hand.
The Bride of Nine Spiders was extremely creepy looking, with blank eyes, pale skin and her body hosting several spiders. In the TV show, she lacks any obviously inhuman traits and is generally a pretty goth with a spider motif.
Mobius M. Mobius is a very plain looking middle-aged man in the comics, but in the show, he's played by movie star Owen Wilson, who still looks rather handsome even with the gray hair and cheesy mustache.
In the comics, He Who Remains has an emaciated, almost skeletal appearance due to having been alive for an unfathomable length of time. In the TV show, as a result of being a Composite Character with Immortus, he's played by a very handsome, youthful looking Jonathan Majors, though dialogue indicates he is still significantly Older Than He Looks.
In the original Marvel Comics, Black Mariah is a comically obese woman hag who weighs around 400 pounds. In the Luke Cage TV series, she's played by the decidedly lovelier (and thinner) Alfre Woodard.
In WandaVision, Agatha Harkness is much younger and more conventionally attractive than her comic counterpart, who is depicted as a gray-haired old woman with wrinkles and a harsh face.