Sum 41 is a Canadian rock band from Ajax, Ontario, Canada. The band was formed in 1996 and currently consists of members Deryck Whibley (lead vocals, rhythm guitar), Tom Thacker (lead guitar, backing vocals), Jason McCaslin (bass guitar, backing vocals) and Steve Jocz (drums). The band signed an international record deal with Island Records in 1999. The band released their debut album, All Killer, No Filler in 2001. The band achieved mainstream success with their first single from the album, "Fat Lip", which reached number-one on the Billboard Modern Rock Tracks chart and remains the band's most successful single to date. All Killer No Filler was certified platinum in the United States, Canada and in the UK. The band has since released four more studio albums: Does This Look Infected?, Chuck, Underclass Hero, and Screaming Bloody Murder.
 They have been nominated for seven Juno Awards and have won twice (Group of the Year in 2002 and Rock Album of the Year for Chuck in 2005). Sum 41 was nominated for a Grammy Award for Best Hard Rock/Metal Performance for the song Blood In My Eyes, however they lost to the Foo Fighters.

Sum 41 was formed by singer-songwriter Deryck Whibley and drummer Steve Jocz, under the name Kaspir after Whibley convinced Jocz to join his band. Jocz was a drummer in another band and Whibley was convinced that "he was the best drummer around". The duo then added Dave Baksh as lead guitarist a year later and after going through several bassists, ended up picking McCaslin to complete their lineup. They decided to change their name for a Supernova show on September 28, 1996 which happened to be the 41st day of summer, hence their current name Sum 41, which still has the same line-up since the name change.