CHICAGO – In a family of vocalists, it was Cleotha Staples’ smooth and velvety voice that helped set apart the sound of the influential and best-selling gospel group The Staple Singers.

Staples, the eldest sister and member of the group her father Roebuck “Pops” Staples started in the 1940s, died Thursday at age 78. She was at her Chicago home and had been suffering from Alzheimer’s disease for the past decade, said family friend and music publicist Bill Carpenter.

The group included sisters Pervis, Yvonne, Mavis and Cynthia, but Cleotha was the backbone, defining herself by being the “strong, silent type,” said Carpenter, author of “Uncloudy Day: The Gospel Music Encyclopedia.”

“When she was young they used to call her granny because she acted like a granny in terms of being wise and always sure of the best thing to do,” Carpenter said.

Staples, known as “Cleedi,” was inducted into the Rock and Roll Hall of Fame with her family in 1999 and received a lifetime achievement award from the Grammys in 2005. The Staple Singers gained a huge audience with their first No. 1 hit “I’ll Take You There” in 1972 and followed with top 40 hits “Respect Yourself,” “Heavy Makes You Happy,” and “If You’re Ready (Come Go With Me).”

The family’s music career had its roots with Pops Staples, a manual laborer who strummed a $10 guitar while teaching his children gospel songs to keep them entertained in the evenings. They sang in church one Sunday morning in 1948, and three encores and a heavy church offering basket convinced Pops music was in the family’s future. The Staple Singers was born.