The 501st Legion (a.k.a. Vader's Fist) is a worldwide organization of Star Wars fans, formed by Albin Johnson and Tom Crews in 1997. The 501st Legion is the world's largest Imperial costuming organization, spanning the entire United States and 59 other countries. The 501st can often be found at promotional events for almost anything related to Star Wars and frequently put their "fame" to use at numerous charity events throughout the year (e.g., Toys for Tots, MDA Telethons, local children's hospitals, etc.).
The fan organization received its first tribute when it was introduced in the Expanded Universe by author Timothy Zahn in both his novel Survivor's Quest and e-book Fool's Bargain, simultaneously released in February 3, 2004. The tribute expanded further with Star Wars: Episode III Revenge of the Sith in 2005, where the legion of blue clone troopers that Darth Vader leads into the Jedi Temple during Operation: Knightfall is designated the 501st in support and merchandising materials. Later, the Legion was also heavily featured in The Clone Wars movie and TV series.
In the 2015 film Star Wars: Episode VII The Force Awakens, a variation of the 501st logo can be seen on a banner in Takodana Castle.
For the live-action television series The Mandalorian, members of the 501st were invited to participate, as the producers did not have enough stormtrooper armor.