In 1969, he left the band to take up a solo career, and released his first album for RCA Records, Rhymes and Reasons. It was not very sucessful, but it contained "Leaving On A Jet Plane", which Peter, Paul and Mary took to number one that same year. He recorded two more albums in 1970, Whose Garden Was This? and Take Me to Tomorrow. Although these albums were still not as successful as those which followed, they would all be 'gold' and later considered to be some of Denver's most classic work.

John's next album, Poems, Prayers and Promises, released the following year, was a breakthrough for Denver in America, largely as a result of the single, "Take Me Home, Country Roads," which went to number two. His career flourished from then on, and hits came fast and furious. In 1972, Denver reached the top ten with his album, Rocky Mountain High. Its title track reached the Top Ten in 1973.

Denver's first marriage was to Annie Martell of St. Peter, Minnesota. Annie was the subject of his much-beloved hit "Annie's Song". In 1974, "Sunshine on My Shoulders" and "Annie's Song" which he wrote for Annie both went to number one, and "Back Home Again" made it to number five. Two number ones followed in 1975, "Thank God I'm A Country Boy" and "Calypso/I'm Sorry," with a top twenty hit, "Sweet Surrender."

Discography