NOTE: The following explanation post contains MAJOR SPOILERS for Quicksilver in X-Men: Days of Future Past and Avengers: Age of Ultron.
Comic book character rights are tricky - especially when it comes to big (and small) screen adaptations. While DC film rights are relatively straightforward, since Warner Bros. owns DC Entertainment (and its subsidiaries), Marvel characters are spread across a variety of film and TV studios. Prior to to the modern Marvel Cinematic Universe (and Disney's acquisition), Marvel properties were producer at other studios - relying on everyone from Lionsgate to Universal Pictures to breath live-action into fan-favorite heroes.
It wasn't until 2008 that Marvel stepped into live-action feature production with the release of Iron Man - laying the foundation for a multi-picture shared universe that, by 2020, will include over 20 films and multiple television series. Despite over $7.5 billion at the global box office to date, Marvel Studios is still beholden to agreements they signed in the '90s - resulting in a complicated Venn diagram of merchandising, licensing, and copyright ownership. While some characters are clearly aligned at specific studios (Wolverine, Captain America, etc), others are split between owners - including Avengers newcomer Quicksilver.
With a new version of Quicksilver appearing in Marvel Studios' Avengers: Age of Ultron less than one year after a different version of the character appeared in 20th Century Fox's X-Men: Days of Future Past, we decided to revisit the complicated history of Marvel movie copyrights - to help explain differences between the two Pietro Maximoffs (aka Quicksilver) and what those differences could mean for future appearances by the character.
Marvel Movie Rights: An Origin Story
The current Marvel and DC movie boom isn't the first time that Hollywood has invested heavily in the superhero genre. Back in the 1980s, comic book movies may not have been nearly as bankable as they are now; yet, there were still plenty of heroes hitting the big screen. However, revolutionary special effects (the ones that would "Make You Believe a Man Can Fly") were not cheap - resulting in a relatively small pool of studios willing to bankroll major superhero projects. In the face of high production budgets, coupled with an interest in expanding awareness for their brand and comic characters, Marvel began selling the film rights to some of their biggest stars: Spider-Man (initially licensed to Cannon Films) was one of the first to be acquired - followed by Blade (at New Line Cinema) and X-Men (20th Century Fox) which were quickly developed as tentpole features.
While Spider-Man sat in development hell (until Columbia Pictures finally got the web-slinger onto the big screen in 2002), the X-Men series set a new standard for comic book movie adaptations - and became a staple of Fox's production line-up. As Marvel Studios (and later Disney) became a powerhouse in the expanding comic book movie genre, the publisher began buying-back, negotiating for, and happily snatching expired rights for characters like Black Panther, Daredevil, Blade, and even Black Widow, whereas other heroes remain unavailable for full re-acquisition.
Nevertheless, not all character rights are as clear-cut - with Namor, and select X-Men, among others, trapped in complicated gray areas - where ownership is not entirely held by a single entity.
Quicksilver's Complicated Copyright
Every hero, studio, and agreement is different, and some details remain sealed away - so our analysis will be limited to the copyright for X-Men/Avengers hero Quicksilver. Unlike key X-Men personnel, like Wolverine or Cyclops, Quicksilver (and his twin sister Scarlet Witch) are also deeply ingrained in Avengers canon - meaning that both 20th Century Fox and Marvel Studios have legitimate right to use the characters in their respective movie universes.
For those unfamiliar with Quicksilver and Scarlet Witch's comic book backstory, their origins hop back and forth between the X-Men and Avengers (as well as X-Factor) series. Recruited by their father (Magneto), the young mutants join his Brotherhood of Evil Mutants - and fight the X-Men on multiple occasions. Though, when Magneto suddenly disappears, the twins return to Europe and attempt to leave their evil ways behind - leading to recruitment by Tony Stark.
The twins, alongside Hawkeye and Captain America, makeup the second generation Avengers team, dubbed: "Cap's Kooky Quartet" - until Scarlet Witch is injured in a battle with Magneto. In the fallout, Quicksilver and his sister attempt to make amends with their father - only to realize that he is truly a villain and the pair rejoin The Avengers. In the years since, both characters appear in X-Men and Avengers titles - forging strong relationships with heroes and villains in each book series.
As a result, certain elements of Quicksilver and Scarlet Witch belong to individual studios - though the characters are shared between Fox and Marvel.
The lines are subtle but, essentially, the Maximoffs can appear in a Marvel movie (Age of Ultron) - as long as there is no mention of Magneto and the twins are not be referred to as "mutants." Similarly, Fox is free to include Quicksilver and Scarlet Witch in an X-Men film (Days of Future Past) but Singer would not be allowed to mention their connection to The Avengers, The Inhumans, or any other Marvel Studios property.