He provided harmony vocals and the occasional lead. He also helped write some of the group's biggest hits, including "Shout," "Fight the Power" and "That Lady."
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 on 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.
Mr. 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; on the funky 1976 cut "You Still Feel the Need," he communicated a carnal urgency.
On recordings like "Fight the Power" and "Livin' in the Life," he and Ronald shared lead vocals with aplomb. 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 Mr. 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 Five Billboard hit, as well as the 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.
In 1989, Mr. Isley retired from the mainstream music industry to pursue his long-deferred dream of a career in the ministry, although he continued to sing in church. He also recorded some gospel songs, and in 1996 released a religious album in 1996 titled "Shouting for Jesus: A Loud Joyful Noise." He and his brothers were inducted into the Rock & Roll Hall of Fame in 1992.
Rudolph Bernard Isley was born on 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.
"I have some very special memories of listening to music with my brothers when we were young," Mr. Isley told the music journalist Leo Sacks for the liner notes to a 1999 boxed set that Mr. Sacks produced, "It's Your Thing: The Story of the Isley Brothers." He added: "Billy Ward and the Dominoes, now that was a group. We idolized them. We got our own thing together because we never lost that harmony group dynamic."
In the group's early days, the eldest brother, Vernon, sang lead. He was killed at age 13 when the bicycle he was riding was struck by a car, and Ronald became the lead singer.
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 over a million copies and came to be acknowledged as a rock 'n' roll classic, spawning covers by Dion, Bruce Springsteen, Garth Brooks and many others. (It was also heard in "National Lampoon's Animal House" and other movies.)
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.
For a brief time in 1964, the Isley Brothers' band included a young guitarist named Jimmy James, who would later be known as Jimi Hendrix.
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). It reached No. 12 on the Billboard chart and No. 3 in Britain. Frustrated by Motown's controlling approach, the brothers, in an unusual move for an African American act at the time, left the label to form their own, T-Neck Records, named after Teaneck, N.J., where they were based.
Switching to a rawer and funkier style influenced by James Brown and Sly Stone, the trio found a new métier, and a new commercial connection. 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; all three contributed instrumental work, and Mr. Jasper also sang. The result was a mostly self-contained band, another rarity for Black artists of the day. Together, they pioneered a unique rock 'n' roll-tinged brand of funk and soul. Over the years, their music covered a wide range of genres, from doo-wop to gospel to quiet-storm ballads.
From 1973 through 1981, all the group's albums went gold, platinum or multiplatinum. Most of the tracks on those albums were co-written by Mr. Isley and the other members.
The group also scored a platinum album in 1986 with "Between the Sheets," whose title track offered their sensual answer to Marvin Gaye's "Sexual Healing." Rudolph Isley shared lead vocals with his brother Ronald on two tracks of that album, the spacey funk number "Way Out Love" and the sensual grind "Slow Down Children."
With the rise of hip-hop, the Isleys' classic material provided the source for more samples than any act other than James Brown and George Clinton's Parliament-Funkadelic.
The death of O'Kelly Isley from a heart attack in 1986 hit Rudolph particularly hard. The group's next album, "Smooth Sailin'" (1987), featured just him and Ronald on the cover and was dedicated to O'Kelly. Two years later, Rudolph quit the music business.
Still, the ever-resourceful, forward-looking group endured and made a successful comeback in 1996 with the album "Mission to Please," buoyed by production and writing from R. Kelly. Rudolph Isley reunited with his brothers for one night in 2004, when the group was given a lifetime achievement honor at the BET Awards.
In March, Rudolph sued his brother Ronald, claiming that he had sought to secure a trademark for the group under his own name exclusively. The suit claimed that the founding members were "at all times" a "common-law partnership."
Marvin Isley died in 2010 from complications of diabetes.
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.
"Music and faith, they just run through our blood," Ms. Isley was quoted as saying in the "It's Your Thing" liner notes. "I may have stopped singing pop music, but I will always be an Isley Brother."
Bernard Mokam contributed reporting.
