Mastodon formed out of Atlanta in 1999 with guitarist Bill Kelliher, drummer Bränn Dailor, bassist/vocalist Troy Sanders, and guitarist/vocalist Brent Hinds. Mastodon's innovative, lyrically astute blend of progressive metal, grindcore, and hardcore helped position the band as a stand out in the New Wave of American Heavy Metal acts of the early 21st century.

The band formed from a mutual admiration of bands such as the Melvins, Black Sabbath, Neurosis, and Thin Lizzy. In 2001 they signed with Relapse Records on the strength of a four-song demo. Their EP Lifesblood arrived that same year, followed by the group's full-length debut, Remission, in 2002. The album was generally well received and created some ground swells in the metal community, but their 2004 release, "Leviathan", really shown the light on the bands sound and gained widespread interest from the metal community and critics. Leviathan is loosely based on author Herman Melville's Moby Dick The album was a turning point in the band's career, appearing on critics' year-end Top Ten lists across the musical spectrum.

Mastodon's newfound popularity helped them get a deal with Warner Bros., but not before fulfilling their contract with Relapse in 2006 by releasing Call of the Mastodon, a remastered version of the group's first two demo EPs, and Workhorse Chronicles, a DVD that chronicled the band's story thus far with interviews and concert footage. The band's third album, Blood Mountain, debuted at number 32 on the Billboard charts and received a Grammy nomination in the Best Metal Performance category for the song "Colony of Birchmen." Blood Mountain marked the band's highest chart peak, and set the stage for its long-awaited 2009 follow-up, Crack the Skye. In 2011, the band released the CD/DVD package Live at the Aragon, which was recorded in Chicago during the Crack the Skye tour. Mastodon followed quickly with new material, taking a step back from their more prog-oriented approach on their fifth studio album, The Hunter. It gave them their biggest commercial success to date, hitting number ten on the Billboard chart.

Later in 2011 Troy Sanders took some time out from the band, forming the metal supergroup Killer Be Killed with Dillinger Escape Plan vocalist Greg Puciato, Soulfly's Max Cavalera, and former Mars Volta drummer Dave Elitch. He worked with the group on and off for the next few years; their debut album was eventually released in 2014. Mastodon was still a priority, however. After touring Europe and South America in 2012, they started work on their sixth album the following year with producer Nick Raskulinecz. The album, eventually titled Once More 'Round the Sun, was released in June 2014, preceded by the sludgy single "High Road."

James Christopher Monger
AllMusic.com