The Joker is a steel roller coaster at Six Flags Discovery Kingdom in Vallejo, California. The ride opened on May 29, 2016, as a rebuild of former wooden roller coaster Roar, adding a new steel track on top of Roar's wooden support structure. This hybrid configuration was implemented by Rocky Mountain Construction and is themed to the Joker, a comic book character villain featured in DC Comics publications. The original Roar roller coaster was constructed by Great Coasters International and opened in 1999.

Six Flags Discovery Kingdom is a 135-acre (55 ha) animal theme park located in Vallejo, California, off of Interstate 80 between San Francisco and Sacramento. The park includes a variety of roller coasters and other amusement rides. Six Flags Discovery Kingdom has been part of the Six Flags chain of amusement parks since 1999.