TITLE: What are examples of mathematical concepts named after the wrong people? (Stigler's law)
QUESTION [34 upvotes]: It's a common observation in Lie theory that Cartan matrices and the Killing form are named after the wrong people; they were discovered by Killing and Cartan, respectively.  I remember learning about many other examples of this phenomenon, but can't think of too many at the moment.  Wikipedia has some examples here and here, but I'm curious about more obscure examples.  
Bonus points for an interesting story behind why the concept was incorrectly named.  Concepts that were deliberately named in honor of another mathematician don't count.

REPLY [3 votes]: A favorite of mine is l'Hôpital's rule. l'Hôpital paid Johann Bernoulli a retainer to keep him updated on developments in calculus and to solve problems he had. Correspondence shows that Bernoulli stated and proved the rule, which l'Hôpital then published.
Heine-Borel was first published by Borel, not Heine. In fact, Heine's name was attached because he was using similar methods to solve related problems. Too bad for both of them that it was actually Dirichlet who was the first recorded to have proved it, but his notes were published posthumously and after Borel's proof. 
Cramer's Rule was published first by MacLaurin, and some believe MacLaurin knew the proof some 20 years before Cramer's publication.