One of the defining voices of American folk music, Campbell had a career which spanned over six decades and he sold over 45 million records.

According to Rolling Stone, in 1968, one of his biggest years, he outsold the Beatles.

"It is with the heaviest of hearts that we announce the passing of our beloved husband, father, grandfather, and legendary singer and guitarist, Glen Travis Campbell, at the age of 81, following his long and courageous battle with Alzheimer's disease," the singer's family said in a statement.