The Lando Society
May his mustache live on forever.
The first PAX prank to get large media attention (NBC News, Kotaku), because no one could tell that the group was joking. This prank favorite has resurfaced a few times at appropriate times after it's first run at PAX Prime 2011: inducting Billy Dee Williams into the Society at ComicCon, and later to his signing at PAX Prime 2015.
Photo credit to Viet Hoang and MetaverseNomad for some of the excellent photography.