Q:

What are examples of mathematical concepts named after the wrong people? ( Stigler's law)

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. 

A:

Q: Who proved the Cayley-Hamilton Theorem? 
A: Frobenius! 
We now have the interesting question: Is this a maximal example of Stigler's law?  That is, can we find distinct persons A, B, and C who are given credit for a result proven by D?  Or A and B who are given credit for a result proven by C and D? 

A:

According to Wikipedia, Markov's inequality is due to Chebyshev, and Chebyshev's inequality is due to Bienaymé. 
On top of that, Hölder's inequality was first proved by Rogers, and Jensen's inequality by Hölder.  What a mess! 

A:

The Frobenius automorphism associated to a prime ideal in a Galois extension of number fields was actually developed by Dedekind, who wrote about it (and the associated ramification groups, later found by Hilbert) in a letter to Frobenius on June 8, 1882.   Frobenius published this construction in a paper in 1896.  Some citations:

Frobenius, Collected Works, Vol.  2, pp.  719--733. 
van der Waerden, Modern Algebra, Vol.  1 (Spring 1966), p. 203. 
Zassenhaus, Canadian Math.  Bulletin 18 (1975), p. 448.