Mastodon was formed in 2000 in Atlanta, Georgia, by Troy Sanders, Brent Hinds, Bill Kelliher, and Brann Dailor. Mastodon is an American sludge metal band. Sludge metal is a sub genre of heavy metal. This sound is a mixture of doom metal and hardcore punk with heavy influences from grunge as well as Southern rock. Mastodon's music features clean vocals compiled with harsh screams and unique, intricate instrumentations. When performing live the band does not interact with the audience as they must concentrate on the technicality of their songs. During their 'Crack the Skye Tour', Mastodon began a large visual show behind the drum set to draw attention from the members. Pink Floyd and Tool have also been known to use this similar presentation. Since formation they have released five albums, each with a particular theme. These albums include: Remission (2000) is based on a fire theme, Leviathan (2004) is based on the novel Moby Dick, Blood Mountain (2006) is based on a search for the 'crystal skull', Crack the Skye (2009) is a tribute to a sister of the band who committed suicide, and The Hunter (2011) is related to the Chinese classical element of wood. With each album release, Mastodon changes the sounds of their vocals. The first albums had more harsh screaming as the latter ones have cleaner tones. The current lineup is as follows: Sanders - bass and vocals, Hinds - guitar and vocals, Kelliher - guitar and backing vocals, Dailor - drums and vocals. They have performed at many major festivals since their formation. Some of these are the Download Festival, Coachella, and Bonnaroo.