The cause was heart failure, his wife, Sheree, said.
Mr. Rainwater's piano playing was curtailed after he lost part of his right thumb in an accident while working in a garage as a teenager. He turned to the guitar, and to singing country music in his twangy baritone, while serving in the Navy during World War II.
"When I went in the Navy, I was so lonesome for my music," Mr. Rainwater said in an interview with Minnesota Public Radio in 1998. "Then I started writing songs, and naturally it fell back to my roots as a boy in Oklahoma, and they turned out to be hillbilly songs."
Draped in a buckskin jacket and beaded headband, he was often billed as Chief Marvin Rainwater though he did not have American Indian heritage, his daughter Judie Rainwater said and became a regular on country music television shows in the 1950s. He also appeared on "The Ed Sullivan Show" and "American Bandstand."
He began recording for MGM Records in 1955. "Gonna Find Me a Bluebird," released two years later, reached No. 18 on the Billboard pop chart. "Whole Lotta Woman," a rockabilly number, reached No. 1 in Britain in 1958 and was sung by Lynn Redgrave in the 1966 film "Georgy Girl." Among his other records were "The Majesty of Love," a duet with Connie Francis released in 1957.
Marvin Karlton Rainwater was born in Wichita, Kan., on July 2, 1925. His family moved frequently, and, he recalled, "Mama took in washing so I could have a piano and take classical lessons."
He parted ways with MGM in the early 1960s and founded his own label, Brave Records. He continued releasing music until the early 1980s and toured until early 2011.
Mr. Rainwater's first two marriages ended in divorce. In addition to his wife, the former Sheree Kay Christensen, and his daughter Judie, from his first marriage, he is survived by a son, Jim, also from his first marriage; two daughters, Barbie and Laura Rainwater, and a son, Wade, from his second marriage; a sister, Patsy Rainwater; a brother, Bob; 11 grandchildren; 11 great-grandchildren and five great-great-grandchildren.