The precursor to BTO was the band Brave Belt, formed in 1970 by Randy Bachman of The Guess Who with Chad Allan (also of The Guess Who), Robbie Bachman and Fred Turner. An original plan included Keith Emerson of The Nice, though he was dropped due to illness. After two moderately successful Brave Belt albums, Allan was replaced by Tim Bachman, the third of the Bachman brothers, and the band changed its name to Bachman-Turner Overdrive; the band released its first, eponymous album under that name in the Spring of 1973.
Their second album with this line-up was Bachman-Turner Overdrive II, and it became a massive hit in the US and their native Canada. It also yielded their best-remembered single, "Takin' Care of Business".
Tim Bachman left to become a record producer and was replaced by Blair Thorton and the first album with the modified lineup, 1974's Not Fragile became a hit, including the #1 single "You Ain't Seen Nothin' Yet". The band continued to steadily produce successful albums through the mid-1970s including Four Wheel Drive and Head On (both 1975).
After the release of Freeways in 1977, Randy Bachman left the group for a solo career and another band, Ironhorse, and what was left of Bachman-Turner Overdrive released a pair of disappointing albums before breaking up. They reunited in the 1980s, leading to a lawsuit as one group, led by Randy, toured as Bachman-Turner Overdrive and another, led by Robbie, toured as BTO. A lawsuit between the brothers resulted.