By 2004, Blink-182, consisting of bassist Mark Hoppus, guitarist Tom DeLonge, and drummer Travis Barker, had achieved significant commercial success in the mainstream. The band had taken a brief break in late 2001 when DeLonge suffered a herniated disc in his back, during which time he collected several darker musical ideas he felt unsuitable for Blink-182, compiling them into a record, "Box Car Racer". The album, recorded with the help of Hazen Street guitarist and longtime friend David Kennedy, was intended as a one-time experimental project but evolved into a full-fledged band upon Barker's involvement. The side project would cause great division between DeLonge and Hoppus, who felt "betrayed." Blink-182 regrouped in 2003 to record and release their eponymous fifth studio album, which, not unlike "Box Car Racer", reflected what critics believed to be a darker, more experimentalist tone.