Rudolph Isley, who held dual roles in the influential vocal group the Isley Brothers as a mellifluous harmony singer and co-writer of many of their greatest hits, died Wednesday at his home in Chicago. He was 84.

He died in his sleep, his brother Ernie said, adding that he was unaware of any health issues his brother might have had.

Isley spent much of his three decades with the Isley Brothers harmonizing with his brother O’Kelly in support of Ronald Isley’s lead vocals. But he also sang lead on some notable tracks. On “I’ve Got to Get Myself Together,” recorded in 1969, his gentlemanly tone gave the song a touch of grace. He also lent a suave lead to the group’s fleeting entry into the disco field, “It’s a Disco Night (Rock Don’t Stop),” which was a club hit in the United States in 1979 and reached the Top 20 in Britain.

The Isley Brothers were always fashionable, and in the 1970s and ’80s, Isley made a fashion statement of his own by wearing hats and furs and carrying a bejeweled cane, giving the Isleys added panache.

He and his brothers wrote a number of pivotal hits, beginning with “Shout,” the group’s 1959 breakthrough, which applied the dynamic of gospel music’s call-and-response to a pop context. They also wrote the enduring political anthem “Fight the Power,” a Top 5 Billboard hit, as well as Top 10 pop hits “It’s Your Thing” and “That Lady.”

Sixteen of the Isley Brothers’ albums cracked the Billboard Top 40, 13 were certified gold, and nine went platinum or multiplatinum.

Isley and his brothers were inducted into the Rock & Roll Hall of Fame in 1992.

Rudolph Bernard Isley was born April 1, 1939, in Cincinnati, the second of six sons of Sallye (Bell) and O’Kelly Isley. He began singing in church as a child, and during his teen years, he and three of the other older Isleys performed together and toured locally.

The Isleys were still quite young when Rudolph, O’Kelly and Ronald moved to New York to pursue a record deal. Contracts with small labels led to one with RCA, one of the biggest in the business, in 1959, and shortly after that, the Isleys wrote and recorded “Shout.” It sold more than 1 million copies and came to be acknowledged as a rock ’n’ roll classic, spawning covers by Dion, Bruce Springsteen, Garth Brooks and many others.

In 1962, the Isleys had a Top 40 hit with their cover of “Twist and Shout,” written by Bert Berns and Phil Medley and originally recorded a year earlier by the Top Notes. Their recording provided a template for the far more popular version recorded by the Beatles in 1963.

The Isleys signed with Motown in 1965.

But despite the label’s reputation for generating hits, they had just one in their brief tenure there, “This Old Heart of Mine (Is Weak for You),” written by the label’s top songwriting team, Lamont Dozier and Brian and Eddie Holland (with Sylvia Moy). Frustrated by Motown’s controlling approach, the brothers left the label to form their own, T-Neck Records, named after Teaneck, New Jersey, where they were based.

Their 1969 single “It’s Your Thing” rose to No. 2 on Billboard’s pop chart and No. 1 on the magazine’s R&B list.

At the start of the 1970s, the group expanded to include the two youngest siblings, Ernie and Marvin, along with Rudolph’s brother-in-law, Chris Jasper.

In addition to his brother Ernie, Rudolph Isley’s survivors include his wife, Elaine Jasper, whom he married in 1958; their children, Rudy Jr., Elizabeth, Valerie and Elaine; his brother Ronald; and several grandchildren.