Country music star George Hamilton IV has died. He was 77 years old.

According to the Grand Ole Opry Hamilton died on late Wednesday afternoon at St. Thomas Midtown Hospital in Nashville, Tennessee. Hamilton had suffered a heart attack last Saturday and was hospitalized. He had been in critical condition since that time. The Opry stated that Hamilton died “with his family by his side.”

Hamilton was a member of the Grand Ole Opry for over 54 years. He was one of the first American country music stars to perform extensively overseas, earning him the nickname “The International Ambassador of Country Music.”

Though Hamilton is best-known for his country crooning, the beginning of his career was very different. During the late 50s Hamilton attended American University in Washington D.C. and began performing pop songs on variety TV show The Jimmy Dean Show. His popularity as a singer grew and he went on to tour with stars such as Buddy Holly and the Everly Brothers.

In 1960 Hamilton made a significant career shift, joining the Grand Ole Opry and performing country music. He saw early success in the genre with hit songs such as “Before This Day Ends” and “If You Don’t Know I Ain’t Gonna Tell You.”

In 1963 Hamilton scored a hit with his album Abilene, which reached number 18 on the U.S. country music charts. The album contains his most famous song to date, “Abilene.” The song reached number 1 on the U.S. country music charts and number 15 on the U.S. pop charts. Hamilton performed the song in the 1963 movie musical Hootenanny Hoot.

With his country music success waning in the late 60s Hamilton took his act overseas. The Grand Ole Opry’s records mark Hamilton as a performer at London’t first International Festival of Country of Music in 1969. Hamilton also performed at other early country music festivals in European countries such as Sweden and Germany.