Most that I can find seem to fit the description of terrorists or hitmen. Are there any that are more of the highly-skilled, master of disguise, mercenary, contract killers, or is this an exaggerated fiction?
I don't know about skilled, but Richard Kuklinski is a well known one, Michael Shannon played him in The Iceman.
If I recall correctly Igor the Assassin is an inspiration for some of these ideas (whether he is real or not).
Solonik is another famous hitman with a pretty wild story.
In a fairly notorious circumstance, Woody Harrelson's Father, Charles, was a hitman of sorts.
The movie The Jackal/The Day of the Jackal (the book as well) inspired the nickname Carlos the Jackal, and not vice/versa. Which is a common misconception.