6) Henry Gyrich
This other important X-Men character was also so hidden away in the movies that you would be hard pressed to notice him, even if you were looking. In X-Men, Senator Kelly is kidnapped when his assistant, Henry Gyrich, is impersonated by Mystique. Elsewhere, a news report mentions that the real Gyrich has been “mauled by a bear” (presumably Sabretooth).
This is a surprisingly brief appearance by a major character in Marvel comics. A perennial thorn in the side of many superheroes, Gyrich was actually the governmental liaison for the Avengers for a time. It’s a shame, then, that he was killed off so quickly, as Gyrich would make for an interesting character for the films to play with.
In more recent years, fans had theorized that Martin Freeman would be playing the role in Captain America: Civil War. However, that isn’t the case, as we now know that he’s actually Everett Ross.