The singer-songwriter and social activist best known as one-third of the folk-music group Peter, Paul and Mary, has died at age 86.

Folk singer Peter Yarrow — writer of the timeless classic "Puff the Magic Dragon" and one-third of the legendary folk trio Peter, Paul and Mary — died Tuesday, a family representative said. He was 86 and had been diagnosed with bladder cancer four years ago.

Peter Yarrow, the singer-songwriter who was one-third of the folk trio Peter, Paul and Mary, has died at age 86, his representative confirmed to ABC News.