Mary Travers, one-third of the hugely popular 1960s folk trio Peter, Paul and Mary, died today after a battle with leukemia, the band's publicist says. She was 72. Travers joined forces with Peter Yarrow and Noel Paul Stookey in the early 1960s. The trio mingled their music with liberal politics, onstage and off. Their version of If I Had a Hammer became an anthem for racial equality. Other hits included Leaving on a Jet Plane and Puff (The Magic Dragon).