Which member of Genesis left before the release of their ninth studio album "...And Then There Were Three..."?

Stephen Richard Hackett (born 12 February 1950) is an English musician, songwriter, singer, and producer who gained prominence as the lead guitarist of the progressive rock band Genesis from 1971 to 1977. Hackett contributed to six Genesis studio albums, three live albums, seven singles and one EP (Extended Play) before he left to pursue a solo career.

"...And Then There Were Three..." is the ninth studio album by the English rock band Genesis. It was released in March 1978 by Charisma Records and is their first recorded as a trio of singer/drummer Phil Collins, keyboardist Tony Banks, and bassist/guitarist Mike Rutherford following the departure of guitarist Steve Hackett. The album marked a change in the band's sound, mixing elements of their progressive rock roots with shorter material, and Collins contributing to more of the group's songwriting.

The album received mixed reviews from critics, but reached No. 3 on the UK Albums Chart and No. 14 on the US 'Billboard' 200. The lead single "Follow You Follow Me" became their highest charting at that point, reaching No. 7 in the UK and No. 23 in the US. The album was certified platinum by the Recording Industry Association of America (RIAA) in 1988 for selling one million copies in the US.