Both Milton and Shakespeare are credited with introducing several new words to the English language.
Shakespeare not only had a huge vocabulary, but it is said that if he didn't have a word that properly executed the meaning he intended, he'd make one up.
Shakespeare has been credited with creating the following words (and more): accommodation, all-knowing, dwindle, fancy-free, frugal, lackluster, and laughable.
Milton's list is much more extensive. Milton made new meanings for existing words, new forms of existing words, new compound words and completely new words.
More examples of each can be found in the links.