An undated photo of Pete Kuykendall. (Bluegrass Unlimited )

Pete Kuykendall, a banjoist, guitarist and songwriter who co-founded the leading bluegrass music publication, Bluegrass Unlimited, and whose composition “I Am Weary Let Me Rest” was featured in the 2000 film “O, Brother Where Art Thou?,” died Aug. 24 at a nursing center in Warrenton, Va. He was 79.

He had diabetes and dementia, said his wife, Katherine “Kitsy” Kuykendall. He was a resident of Marshall, Va.

“Nobody had a greater hand in promoting bluegrass not only to aficionados, but to a wider audience,” said ethnomusicologist Kip Lornell, author of the forthcoming book “Capitol Bluegrass: Hillbilly Music Meets Urban Culture in Washington D.C.” “He was an accomplished but not virtuoso musician. His virtuosity was as an entrepreneur.”

Bluegrass Unlimited began in 1966 as a mimeographed newsletter. Four years later, with money from his publishing company, Wynwood Music, Mr. Kuykendall turned the fan publication into a glossy monthly magazine that sports concert and record reviews, tour itineraries and typically, two or three in-depth profiles of musicians.

Mr. Kuykendall began his career in the early 1950s, playing banjo with a husband and wife duo, Benny and Vallie Cain. He performed as Pete Roberts because the Cains had trouble pronouncing his Dutch surname, Kuykendall.

He briefly replaced banjoist Bill Emerson in the newly formed Country Gentlemen in 1958 and appeared on some of their earliest recordings for Starday Records. Through its many personnel changes, the group helped broaden the audience for bluegrass music by adding modern folk songs by such writers as Bob Dylan and Gordon Lightfoot to their repertoire.

Though Mr. Kuykendall was replaced by Eddie Adcock in the group, he remained a significant influence by contributing his own songs to their concert sets, engineering many of their records in his Falls Church, Va., studio and even picking on a few records. He also performed and recorded with Red Allen and the Kentuckians in the mid-’60s, a group that featured the virtuoso mandolinist Frank Wakefield.

His compositions included the bluegrass standards “Journey’s End,” first recorded by Allen’s group; and “Remembrance of You” and “I Am Weary Let Me Rest,” which were recorded by the Country Gentlemen. The last, a gospel song, was reprised by the Cox Family in the soundtrack to “O, Brother Where Art Thou?,” a film by the Coen Brothers starring George Clooney.

The Country Gentlemen’s 1963 album “Folk Session Inside,” recorded in Mr. Kuykendall’s home studio, features Mr. Kuykendall’s guitar work on the song “The Galveston Flood” and on banjo on “This Morning at Nine.”

“He would set the controls, start the tape running, then walk away from the console to play his part,” said Tom Gray, then the bassist for the Country Gentlemen.

Mr. Kuykendall also recorded country blues men Mississippi John Hurt, Skip James and the Rev. Robert Wilkins, none of whom had recorded since the 1920s and ’30s, for the record labels Melodeon and Piedmont.

Through Wynwood Music, he secured copyrights for their songs that had not been previously copyrighted. Mr. Kuykendall’s share of royalties from the Rolling Stones’ cover of Wilkins’s “Prodigal Son” and a cover of James’s “I’m So Glad,” by Eric Clapton’s power trio Cream enabled him to leave his job as a sound engineer at WETA-TV in the early 1970s and turn Bluegrass Unlimited into a glossy publication.

In 1985, Mr. Kuykendall co-founded the International Bluegrass Music Association, a trade group that helps ailing pickers with medical expenses and educates younger musicians in the business aspects of music.

Peter Van Kuykendall was born in Washington on Jan. 15, 1938, and grew up in Arlington, Va. He played clarinet in his junior high concert band but later gravitated toward boogie-woogie piano and bluegrass. In addition to banjo and guitar, Mr. Kuykendall played mandolin, string bass and fiddle.

He received a certificate in radio and electronics from the old Capitol Radio and Electronics Institute. His day jobs included a stint at the Library of Congress recording division, where he transferred field recordings from fragile discs and cylinders to magnetic tape.

His first marriage, to Ann Lane, ended in divorce. His second wife, Marion Cain, died in 1984. A son from his second marriage, William Kuykendall, died in 1982.

Survivors include his wife of 29 years, the former Katherine Easton of Marshall; a son from his first marriage, Glenn Kuykendall of Nashville; two daughters from his second marriage, Ginger Kuykendall Allred of Mount Airy, N.C., and Sharon McGraw of Culpeper, Va.; four stepchildren; two grandchildren; and seven great-grandchildren.

“He struggled through much of his life with a bipolar condition that he fought to control, coping with mood swings that could bring on either severe depression or wild optimism,” folk music historian Dick Spottswood wrote in a forthcoming obituary for Bluegrass Unlimited.

“Fortunately the situation wasn’t all negative,” Spottswood added. “Some of Pete’s best ideas emerged from moments of euphoria, and his conviction that he could do anything worth doing if he tried hard enough and smart enough.”