Ray Collins, a singer whose dispute with one guitarist led him to hire another, Frank Zappa, with whom he would go on to form the avant-garde rock group the Mothers of Invention, died on Monday in Pomona, Calif. He was in his mid seventies His death followed his admission to Pomona Valley Hospital Medical Center about a week earlier for cardiac arrest, according to local news accounts. Mr. Collins entered the national spotlight with the Mothers of Invention, an outlet for Mr. Zappaâ€™s unique sense of humor and challenging, unorthodox compositions. But his musical beginnings were more mainstream. In the mid-1960s Mr. Collins was singing falsetto in a rhythm-and-blues cover band called the Soul Giants when things soured between him and the bandâ€™s guitarist, Ray Hunt. Mr. Collins fired Mr. Hunt and replaced him with Mr. Zappa. Precisely how he delivered the news of the firing is unclear. Mr. Collins â€œpunched his lights out,â€ Mr. Zappa told the television host Mike Douglas in the 1970s. â€œHe was out of the band and they needed somebody to come in and take over for a while, so I went down there and sat in with them and I thought they were real good.â€ In Mr. Collinsâ€™s version of the events he threw no punches, but Mr. Zappa did indeed take over the band. Mr. Zappa urged his band mates to perform original material â€” his own â€” and the Soul Giants changed their name, first to the Mothers and later to the Mothers of Invention. The shift in direction eventually led to recognition, a recording contract, some truly original music and a devoted following, if not rock stardom. Mr. Collins, who shared a love for doo-wop with Mr. Zappa, was the lead singer for the bandâ€™s debut album, â€œFreak Out!â€ (1966), which mixed satirical lyrics with music that ranged from straightforward rock to atonal experimentation, and its follow-up, â€œAbsolutely Freeâ€ (1967). He quit the band after that recording, though he returned for â€œCruising With Ruben & the Jets,â€ a doo-wop concept album, and sang on some of Mr. Zappaâ€™s later recordings.