Three Days Grace is a Canadian rock band formed in Norwood, Ontario in 1997. Based in Toronto, the band's original line-up consisted of guitarist and lead vocalist Adam Gontier, drummer and backing vocalist Neil Sanderson, and bassist Brad Walst. In 2003, Barry Stock was recruited as the band's lead guitarist, making Three Days Grace a four-member band. In 2013, Gontier left the band and was replaced by My Darkest Days' vocalist Matt Walst, who is also bassist Brad Walst's brother.

Three Days Grace has its origins in a five-piece band called "Groundswell", formed in Norwood, Ontario, in 1992. Groundswell released one full-length album, Wave of Popular Feeling. The band's line-up consisted of lead vocalist Adam Gontier, drummer Neil Sanderson, bassist Brad Walst, lead guitarist Phil Crowe, and rhythm guitarist Joe Grant. Most of the members were attending high school when the band formed. By the end of 1995, the band had broken up.  In 1997, Gontier, Sanderson, and Walst regrouped as "Three Days Grace". According to Gontier, the name refers to a sense of urgency, with the question being whether someone could change something in their life if they had only three days to make a change. Once in Toronto, the band became acquainted with local producer Gavin Brown. The band gave him several years of material which they had created, and he "...picked out what he called 'the golden nuggets'", according to Gontier. Brown and the band polished the songs, and created a demo album, which they gave to EMI Music Publishing Canada. The record label wanted to hear more material, and with Brown producing, the band created the song, "I Hate Everything About You", which attracted the interest of several record labels. The band was soon signed to Jive Records after being sought out by the company's president.  The band moved to Long View Farm, a studio in North Brookfield, Massachusetts, to record their debut album. The self-titled album was finished in Woodstock, New York and released on July 22, 2003.  It was met with mixed to favourable reviews. Dave Doray of IGN said of the album, "Mistakes? There's not many." Allmusic reviewer Heather Phares said that on Three Days Grace, "the band's focus and adherence to alt-metal's formulas - coupled with tight songwriting and some unexpectedly pretty choruses - results in a strong tracks  [sic] that are more memorable than the work of many of their peers". She did criticize the album for its simplicity, concluding, "Three Days Grace are definitely one of the most accessible alt-metal bands of the 2000s; they just need to add some more distinctiveness to their sound."  To support the eponymous album, in 2003 Three Days Grace released its first single, "I Hate Everything About You" (the song whose demo had gotten the band its record deal). The song received heavy airplay and rapidly became a widely recognizable song, and was labelled as the band's "breakout hit". After Barry Stock joined as lead guitarist in late 2003, Three Days Grace toured continuously and extensively for nearly two years in support of their major label debut. The album peaked at number nine on the Canadian Albums Chart and number 69 on the Billboard 200, and was certified platinum in the U.S. by the RIAA in December 2004 and double platinum in Canada by the CRIA.

How many of them were in it initially?
The band's line-up consisted of lead vocalist Adam Gontier, drummer Neil Sanderson, bassist Brad Walst, lead guitarist Phil Crowe, and rhythm guitarist Joe Grant.