Mine's Aachenosaurus. It's such an interesting (if sad) story about how science works.

From Wikipedia: Independently in 1887, the name Aachenosaurus was created by the scientist (and abbé) Gerard Smets based on fossilized fragments of material that he thought were jaw fragments from a duck-billed dinosaur (a hadrosaur). However, the fossils turned out to be petrified wood, to the great embarrassment of the discoverer.

So while he advanced science by reporting his discovery and advancing a theory about what it was, he will forever be remembered mostly for how very wrong he was.