Now that Gram Parsons has been mentioned, here's more:
Gram was brought into The Byrds by bassist Chris Hillman, to replace the recently-departed (from The Byrds, not Earth) David Crosby. Gram (real name Ingram Cecil Parsons III) was a student at Harvard, playing music in a Folk group. Chris, a former member of Bluegrass group The Hillmen (guess he was the leader ;-) knew of Gram, and between the two turned The Byrds from a Folk-Rock group to a pretty hardcore Country band with the Sweethearts Of The Rodeo album.
Chris and Gram then left The Byrds and started The Flying Burrito Brothers. After a coupla FBB albums, Gram left and started his solo career, bringing along Emmylou Harris, a singer he had heard at a Folk club in the Washington D.C. area. Gram was a huge George Jones and Merle Haggard fan, and the two albums he made before he overdosed in Joshua Tree are classics. Gram and Keith Richards became close friends, and Gram's influence on Keith can be heard on The Stones' "Country Honk" track on Let It Bleed.
Gram and Emmylou's recording of "Love Hurts" is well known, thought by many to be a Gram song. It is actually a song first recorded by The Everly Brothers, written by Felice & Boudleaux Bryant.