BEACON, N.Y. — Toshi Seeger, folk singer Pete Seeger’s wife of 70 years and a close partner in his social and environmental activism, has died. She was 91.

Longtime family friend Thom Wolke confirmed that she died Tuesday night at the couple’s home in Beacon in New York’s Hudson Valley. The cause of death was not immediately known.

Never famous like her 94-year-old husband, friends say Toshi Seeger was an equal who perfectly complemented Pete Seeger’s idealism.

“To understand Pete, you have to know Toshi,” Wolke said. “They were the ultimate yin and yang. Where Pete was … the artist, Toshi kept him grounded.”

Toshi Seeger was particularly active with the Hudson River Sloop Clearwater, an environmental group. Tao Rodriguez-Seeger said his grandmother was a pioneer in festival production who played a key role in Clearwater’s annual festival.