The Fox Legal Tangle Behind Quicksilver
Because Fox owned the X-Men film rights and Quicksilver is technically Magneto's son, Marvel had to walk a tightrope. The deal struck between the studios meant this version of Pietro could never be called a mutant, and no line could tie him back to the X-Men or his comic dad, even though Fox had their own speedster running around in Days of Future Past at basically the same time.
