Author Usurpation

A work so iconic, it defines the creator. And makes people forget that He Also Did (other works, which you wouldn't believe if you didn't know).

In most cases, authors that create a great work and several lesser-known works can still be associated with all of them. However, if the work is popular enough, it overshadows all other aspects of their career. In extreme cases, the work becomes synonymous with the author's name.

For the actor version, see I Am Not Spock.

Comic Books

 * Alan Moore and Watchmen.

Film

 * George Lucas and Star Wars.

Literature

 * George Orwell and 1984. Despite being responsible for any number of other exceptional books, the word "Orwellian" forever refers to the totalitarian, oppressive/suppressive government present in 1984; evidence for it is right here on the site. It doesn't help that his second most famous book, Animal Farm concerns almost all of the same themes.
 * HP Lovecraft is another extreme example; Lovecraftian basically means Cosmic Horror Story and/or Eldritch Abomination.
 * To complete the trifecta, Niccolo Machiavelli's non-fiction essay The Prince has forever ensured that "Machiavellian" will always be a synonym for amoral behavior in the pursuit of absolute power, despite the fact that Machiavelli himself was staunchly pro-republican.
 * Orson Scott Card and Ender's Game. He also wrote a bunch of sequels and several other series.
 * CS Lewis and Narnia.
 * JRR Tolkien and The Lord of the Rings.
 * Douglas Adams and The Hitchhikers Guide to The Galaxy.
 * L Frank Baum and The Wonderful Wizard of Oz.
 * Sir Arthur Conan Doyle and the Sherlock Holmes stories, reportedly to the author's chagrin.
 * AA Milne and Winnie the Pooh.
 * Mary Shelley and Frankenstein.
 * J.M. Barrie and Peter Pan.

Live Action Television

 * Gene Roddenberry and Star Trek.

Video Games

 * Hideo Kojima and Metal Gear Solid, to his annoyance.
 * Bungie, despite making ground-breaking series such as Marathon and Myth, will forevermore be known as the studio that created the Halo series.