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.

Peter Yarrow, the pioneering folk musician who found massive success as part of the musical trio Peter, Paul, and Mary, has died at the age of 86, according to the Associated Press.

Peter Yarrow, whose Peter, Paul and Mary trio helped bridge folk music into the pop world with such hit songs as "Puff the Magic Dragon" and "If I Had a Hammer," has died at 86. He had bladder ...

NEW YORK, NY – MARCH 23: Peter Yarrow attends the “While We’re Young” New York Premiere at Paris Theater on March 23, 2015 in New York City. (Photo by Dimitrios Kambouris/Getty Images ...

(AP Photo/Kathy Willens, File) FILE – Peter Yarrow attends the premiere of “While We’re Young” at the Paris Theatre on March 23, 2015, in New York. (Photo by Charles Sykes/Invision/AP ...