People who saw last year's "X-Men: Days of Future Past" surely remember the fleet-footed young mutant who helped Professor X, Magneto and Wolverine in the kitchen of the Pentagon. That is Quicksilver. And people who see "Avengers: Age of Ultron" will see a fleet-footed young man who was experimented on by Hydra. That too, is Quicksilver. The first is played by Evan Peters, previously best known for his role in "Kick-Ass." The second is played by Aaron Taylor-Johnson, star of "Kick-Ass."

So what's the deal? Why are there two different actors playing the same character in two different films based on Marvel Comics? As usual, it all comes down to money and large corporations.

Marvel has the rights to its characters, of course. It sold the film and television rights for X-Men and the mutants to Fox, and the rights to Spider-Man to Sony, but it retained the film and television rights for The Avengers.

So, here's where it gets tricky. Quicksilver, as well as Scarlet Witch, first appeared in the fourth issue of "The X-Men" in March 1964, created by Stan Lee and Jack Kirby. They were villains at first, but a little more than a year later became superheroes in ? The Avengers, joining the team in the 16th issue of "The Avengers" in May 1965. The mutant characters have been Avengers ever since.

As "X-Men" and "The Avengers" have made the jump to the big screen, Marvel and Fox were able to reach an agreement allowing for both film franchises to feature the characters, but with one big difference: The Quicksilver and Scarlet Witch in "Avengers: Age of Ultron" are not mutants.

Got it?