SAN FRANCISCO–In 1970, 20-year-old student Bill Sagan had his first real brush with rock and roll history at an early Led Zeppelin concert at Chicago’s fabled Aragon Ballroom.

Now the entrepreneur owns one of rock’s biggest treasure troves of recorded shows by Zeppelin and other history-making bands, and he’s beginning to share it freely online.

Since 2002, Sagan has owned the full archives of legendary promoter Bill Graham, whose concerts featuring performers such as the Grateful Dead, Jefferson Airplane, Jimi Hendrix and others helped define the late 1960s and early ’70s. Sagan began putting excerpts from these concerts, many of which have never been released, online by way of a free Internet radio station on his company’s Wolfgang’s Vault site.