Question: Johnny Cash is a part of what unique statistic?
Context: "Forty Shades of Green" is a song about Ireland, written and first performed by American country singer Johnny Cash.  Cash wrote the song in 1959 while on a trip to Ireland; it was first released as a B-side of the song "The Rebel–Johnny Yuma" in 1961.  It is also included in two of Cash's albums: "Ring of Fire: The Best of Johnny Cash", released on Columbia Records in 1963, and "Johnny Cash: The Great Lost Performance – Live at the Paramount Theatre, Asbury Park, New Jersey", recorded live in 1990 and released in 2007. Hello, I'm Johnny Cash is the 33rd album by American country singer Johnny Cash, released on Columbia Records in 1970 (see 1970 in music).  "If I Were a Carpenter", a famous duet with Cash's wife, June Carter Cash, earned the couple a Grammy Award for Best Country Performance by a Duo or Group with Vocal in 1971 (see Grammy Awards of 1971); the song also reached No. 2 on the Country charts.  This album also includes "To Beat the Devil", the first Kris Kristofferson song covered by Cash; the two would later collaborate numerous times, most famously on "Sunday Mornin' Comin' Down".  "See Ruby Fall" and "Blistered" were also released as singles, and the album itself reached No. 1 on the country charts and No. 6 on the pop charts.  It was certified Gold on 1/29/1970 by the R.I.A.A.  The album has been released on CD (Sony Music, Original Album Classics, along with "The Johnny Cash Show" and "Man In Black") and it has been made available on official download sites.  This album is not to be confused with a best-of cd that has the same name. The Carter Family is a traditional American folk music group that recorded between 1927 and 1956.  Their music had a profound impact on bluegrass, country, Southern Gospel, pop and rock musicians as well as on the U.S. folk revival of the 1960s.  They were the first vocal group to become country music stars.  Their recordings of songs such as "Wabash Cannonball", "Can the Circle Be Unbroken", "Wildwood Flower", "Keep On the Sunny Side" and "I'm Thinking Tonight of My Blue Eyes" made these songs country standards.  The latter's tune was used for Roy Acuff's "The Great Speckled Bird", Hank Thompson's "The Wild Side of Life" and Kitty Wells' "It Wasn't God Who Made Honky Tonk Angels", making the song a hit all over again in other incarnations. Wildwood Flower is the last solo album from June Carter Cash.  It was released in 2003 on the Dualtone record label, four months after her death and only a few days before the death of Johnny Cash, who provides backing vocals, making this the final release of his lifetime.  It was produced by their son, John Carter Cash.  The album's opening track, "Keep on the Sunny Side" was a Carter Family anthem that June Carter Cash had previously recorded twice with Johnny Cash: for the 1964 Carter Family album of the same title, and for the 1974 Johnny Cash album "The Junkie and the Juicehead Minus Me".  "The Road to Kaintuck", written by June, had previously been recorded by her husband on several occasions for Columbia Records.  The medley of "Church in the Wildwood"/"Lonesome Valley" had been a regular part of Johnny Cash concerts in the 1970s. The Johnny Cash Family Christmas is the 41st overall and second Christmas album by country singer Johnny Cash, released on Columbia Records in 1972).  It is his second Christmas album, the first one being the 1963 release entitled "The Christmas Spirit".  The album includes less original Cash material than its predecessor and contains narrations and dialogue featuring his family and friends, between tracks.  In all, three songs were written or co-written by Cash, while two, "Christmas as I Knew It" and "Silent Night", had been featured on "The Christmas Spirit" ("Silent Night" would, in fact, be featured on all four Johnny Cash Christmas albums).  June Carter Cash, Marshall Grant, Tommy Cash, Harold Reid, Larry Butler (who was both Cash's piano player and record producer at this time), Maybelle Carter, Anita Carter, Carl Perkins and Lew DeWitt are among those featured on the album. Ring of Fire: The Best of Johnny Cash is the sixteenth album in total by the singer-songwriter Johnny Cash, released on Columbia Records in 1963 (see 1963 in music).  This album collects tracks from singles and an EP released between 1959 and 1963, Cash's first years on the Columbia label, and marked the first release of these tracks in LP format, with the exception of "I Still Miss Someone," which had previously appeared on the 1958 album "The Fabulous Johnny Cash". " Ring of Fire", one of Cash's most famous tracks, made its first LP appearance here.  "Ring of Fire" was the first #1 album when Billboard debuted their Country Album Chart on Jan. 11, 1964.  It was certified Gold on 2/11/1965 by the RIAA.  It stands as the only Columbia "greatest hits" collection to be included in the "" box set. Kenneth Jones (1952–1969), was the son of Helen Myrl Carter (of country music's Carter Family) and of Glenn Jones.  He is best remembered for a song he wrote called "Sing A Traveling Song" which appeared on Johnny Cash's albums "Hello, I'm Johnny Cash" and "Johnny Cash at Madison Square Garden".  Kenneth was Cash's nephew-in-law.  Cash's second wife, June Carter Cash, was Helen's sister.  Kenneth, or Kenny as he was also known, wrote many songs and was a talented musician.  At the time of his death he was under contract with Monument Records and appeared destined for a highly successful career.  Following his death the Carter Family recorded one of his songs, "2001 Ballad to the Future".  A few have noted the lyrics as being eerily prophetic of the September 11, 2001 terrorist attacks on the United States which took place more than thirty years after the song was written. Johnny Cash Country Christmas is a Christmas album and 78th overall album by American country singer Johnny Cash, released on Delta Records in 1991 (see 1991 in music), in-between Cash's contracts with Mercury Records and American Recordings.  It came out in two different Versions with different cover art.  It contains 15 or 13 songs, all Christmas classics and traditional holiday songs.  A number of songs (such as "Blue Christmas", "Silent Night" and "Joy to the World") had previously been recorded by Cash - multiple times, in the case of "Silent Night" - for previous Christmas albums.  It was also released on the LaserLight label in 1992.  The 15-track version includes two additional Christmas songs, "White Christmas" and "I'll Be Home for Christmas".  Four tracks do not feature Cash but instead feature vocals by his wife, June Carter Cash and the Carter Family.  This was the last Johnny Cash release within his lifetime to feature the Carters, who had been a staple of his live show and studio recordings since the early 1960s, as the sisters would not participate in his subsequent work for American Recordings; nor would June Carter Cash, though a 2000 private release, "Return to the Promised Land", would feature her alongside her husband. The Roadshow Revival is a Johnny Cash Tribute Festival held at Mission Park in Ventura, California in June.  The location of the Event is in close proximity to Johnny Cash's home and office in Casitas Springs and Ventura.  It is produced by Ross Emery and Johnny Cash's daughter, Cindy Cash and features Outlaw Country acts, Rockabilly bands, a Johnny Cash Memorabilia Gallery, Pin-Up Girl Pageant, and a car and bike show. Valerie June Carter Cash (June 23, 1929 – May 15, 2003) was an American singer, songwriter, actress, dancer, comedian, and author who was a member of the Carter Family and the second wife of singer Johnny Cash.  Prior to her marriage to Cash, she was professionally known as June Carter and occasionally was still credited as such after her marriage (as well as on songwriting credits antedating it).
Answer: first vocal group to become country music stars