Steve Harwell, the former lead singer of the rock band Smash Mouth, which was best known for its 1999 hit “All Star,” died on Monday. He was 56.

His death, at his home in Boise, Idaho, was confirmed by the band’s manager, Robert Hayes, who said the cause was liver failure.

Smash Mouth was founded in 1994 in San Jose, Calif., and was made up of Mr. Harwell, the guitarist Greg Camp, the drummer Kevin Coleman and the bassist Paul De Lisle. Its first success came with the song “Walkin’ on the Sun,” from the band’s debut album, “Fush Yu Mang” (1997).

An upbeat track with a dark undertow, calling to mind both the Doors and contemporary ska-punk, “Walkin’ on the Sun,” with songwriting credits going to all four band members, went into steady rotation on MTV and topped Billboard’s alternative chart.

The song’s music video laid out the band’s aesthetic and attitude. Dressed in short-sleeve shirts and shades, with fedoras and soul patches, the four members looked…