Don Everly, whose soaring harmonies and aggressive rhythm guitar work as part of the Everly Brothers duo with his younger brother, Phil, influenced generations of rock performers, died Aug. 21 at his home in Nashville. He was 84.

His daughter Erin Everly confirmed the death but did not provide an immediate cause.

The musical harmony of the Everly Brothers, rooted in a long tradition of fraternal country duos, could be heard in many acts that followed them after their popularity waned in the mid-1960s, including the Beatles, Simon and Garfunkel, and the Hollies. At their peak, the brothers nearly rivaled Elvis Presley in commercial power.

Their first million-seller, “Bye Bye Love” (1957), a bouncy synthesis of country and rock buoyed by four guitars, made them one of the top acts in the country and led to appearances on variety programs, including TV’s “The Ed Sullivan Show” and radio’s “The Grand Ole Opry.” They had 31 records in the Billboard Hot 100, with 12 in the top 10.

Mr. Everly wrote some of their most popular songs, among them “(’Til) I Kissed You” (1959), “Cathy’s Clown” (1960) and “So Sad (To Watch Good Love Go Bad)” (1960). Phil Everly’s compositions included “When Will I Be Loved” (1960), later covered by Linda Ronstadt.

The brothers benefited from a relationship with the Nashville husband-and-wife songwriting team of Boudleaux and Felice Bryant, beginning with “Bye Bye Love.” The Bryants’ lyrics for songs such as “All I Have to Do Is Dream,” “Bird Dog” and “Wake Up Little Susie” — a song that featured Mr. Everly’s percussive guitar work — captured the longing and drama of teenage love without trivializing it.

The Everly Brothers also covered rhythm-and-blues songs such as Little Richard’s “Lucille” and Ray Charles’s “This Little Girl of Mine” in their country vocal style. Their ballads included the enduring “Let It Be Me” (1960), translated from the French chanson “Je t’appartiens” by singer Gilbert Bécaud.

They recorded their early hits in Nashville with A-team session players such as pianist Floyd Cramer and guitarist Chet Atkins. Atkins, also their producer, placed their voices against an understated drum beat, with the brothers’ high-tuned acoustic guitars at the front of the mix. The Gibson company marketed a signature Everly Brothers folk guitar with an all-black finish.

After a six-month stint in the Marine Corps Reserve, Don and Phil found their careers slowing down. The duo charted only sporadically after 1962. They quarreled with their publishing and management company, Acuff-Rose, a move that restricted their access to new songs from the Bryants.

Mr. Everly, addicted to uppers and downers — Ritalin and vitamins to keep him awake and barbiturates to help him sleep — twice attempted to kill himself with an overdose during an English tour in 1962. When they returned stateside, he received electroshock therapy, which he said blocked his ability to write songs for several years.

“People didn’t understand drugs that well then,” he told Rolling Stone in 1986. “They didn’t know what they were messing with.”

The brothers’ personal relationship was less harmonious than their music. Their relentless performing over 30 years magnified their sibling rivalry and simmering resentments. They endured long periods when they sang together but wouldn’t talk to each other.

When interviewers could get them in the same room, Mr. Everly, the more gregarious of the two, tended to dominate the conversation. They also fractured on politics, with Phil a conservative and Don a liberal.

Both singers attempted solo careers, with limited success. In 1970, Mr. Everly toured to promote his first solo album with Lindsey Buckingham, then the Everly Brothers’ lead guitarist and later a member of Fleetwood Mac, singing harmony. After an unreceptive audience demanded oldies such as “Bye Bye Love,” he canceled the tour.

Although they would reunite in the 1980s, the Everly Brothers officially broke up after a 1973 concert in Buena Park in Orange County, Calif. Mr. Everly, who had given notice to his brother, came onstage drunk. Irate, the venue’s manager stopped the duo in the middle of the show, causing Phil Everly to smash his guitar and walk offstage.

“It was really a funeral,” Mr. Everly later told Rolling Stone. “People thought that night was just some brouhaha between Phil and me. They didn’t realize we had been working our buns off for years. We had never been anywhere without working; had never known any freedom. We were just strapped together like a team of horses. . . . It was one of the saddest days of my life.”

Isaac Donald Everly was born Feb. 1, 1937, in Brownie, a town in Kentucky’s coal mining region. His father, Ike, a miner turned itinerant guitarist, sang with his wife, Margaret. The family eventually settled in Iowa, where the boys began performing on their father’s radio show, billed as “Little Donnie” and “Baby Boy Phil.”

Don Everly was a hitmaking songwriter in his teens, with “Thou Shalt Not Steal” and “Here We Are Again,” recorded by Kitty Wells and Anita Carter, respectively. In 1955, the brothers moved to Nashville to pursue careers as country singers. Their first hit, however, came a few years later for a small New York pop label, Cadence Records. “Bye Bye Love” had reportedly been turned down by four other performers.

With more hits to their credit, the duo signed in 1960 with Warner Bros. records for $1 million, to be paid over 10 years. At the time, it was an unprecedented sum for a rock-and-roll act.

Although best known for their singles, the Everly Brothers received critical praise for several albums. “Songs Our Daddy Taught Us” (1958), their folk album, consisted primarily of traditional Appalachian songs sung to the sparse accompaniment of the brothers’ guitars. “Two Yanks in London” (1966), an attempt to update their sound, featured compositions and accompaniment from longtime admirers the Hollies. “Roots” (1968), which combined vintage Everly family radio shows with newer recordings, is considered one of the finest early country rock albums.

The brothers also served as summer replacement hosts for Johnny Cash in 1970 on the ABC variety program “Johnny Cash Presents the Everly Brothers.”

In the 1970s, Mr. Everly recorded two more solo albums and did session work as a harmony singer behind Emmylou Harris. When Phil Everly’s 1983 duet with Cliff Richard, “She Means Nothing to Me,” topped the British charts, the duo was persuaded to do a reunion concert at London’s Royal Albert Hall.

They released the album “EB 84” (1984) and, from that, had a minor hit single with “On the Wings of a Nightingale,” written by Paul McCartney. Two years later, they were inducted into the Rock and Roll Hall of Fame and scored a top-20 country hit with the title track from the album “Born Yesterday.” According to producer Dave Edmunds, on their later recordings, Phil preferred to record his harmonies separately after Don recorded his lead.

Both brothers sang on the title track of “Graceland” for another longtime admirer, Paul Simon. Simon and Garfunkel, who began their career as an Everly-style duo by the name of Tom and Jerry, later covered “Bye Bye Love” and had the brothers as guests for their 2003-2004 reunion tour.

The Everly Brothers’ honors included a lifetime achievement Grammy Award in 1997 and induction into the Country Music Hall of Fame in 2001.

Mr. Everly’s marriages to Mary Sue Ingraham, model and actress Venetia Stevenson and Karen Prettyman ended in divorce. In 1997, he married Adela Garza.

In addition to his fourth wife, survivors include a daughter from his first marriage, Venetia; three children from his second marriage, Stacy, Erin and Edan; his mother, Margaret Everly of Nashville; and six grandchildren.

Phil Everly died in 2014 at 74. Mr. Everly attributed their musical success to a shared instinct and, in the later years in his life, even expressed gratitude for being musically reunited with his brother.

“I think that what Phil and I have done is something that took being brothers, growing up together and having worked together all these years,” he told the Daily Telegraph of Sydney in 1998. “We have separate lives, but when we walk out onstage, it comes back, and it amazes me that we can do it. It’s like riding a bicycle. I don’t know how it’s done but I know it can be done.”