10) J.A.R.V.I.S.
Comic Books: First appearing in the comics in 1964, Edwin Jarvis is the faithful English butler of the Stark household. For decades, the character also provided a loyal helping hand to Earth’s Mightiest Heroes as he served them in their Avengers Mansion headquarters. He’s such a beloved part of their unit that Captain America’s claimed that he “is as much an Avenger as I am.”
MCU: When 2008’s Iron Man came out, the Jarvis character was revised from top to bottom. In order to avoid comparison with Batman’s butler Alfred Pennyworth, Edwin Jarvis was out and in came J.A.R.V.I.S. (Paul Bettany), Tony’s handy artificial intelligence that pilots his Iron Man armour.
The character took another unique turn when J.A.R.V.I.S. was merged with the android superhero Vision. In the movies, he’s an evolved version of the A.I. whereas Vision is simply a creation of Ultron’s in the comics.
The human Jarvis did eventually make it into the MCU, though, as James D’Arcy played Howard Stark’s butler in the 1950s-set Agent Carter.