One of America's leading opera directors, Sarah Caldwell, has died.

Caldwell died Thursday of heart failure in Maine, at the age of 82.

The founding director and conductor of the Opera Company of Boston, Caldwell was hailed as a visionary for staging works considered too challenging or obscure by more established opera houses.

In 1976, she became the first woman to conduct at the Metropolitan Opera in New York, the nation's leading opera house, shortly after being hailed in a Time magazine cover story as "Music's Wonder Woman."

She was known for engaging operatic stars as well as encouraging unknowns.  She worked with Soviet artists during the Cold War, and was praised for her pioneering work in ignoring ethnicity and race when casting her works.

Caldwell was awarded the National Medal of the Arts in 1996.

As director, conductor, administrator and chief fundraiser, the larger than life Caldwell was often stretched thin, working around the clock in the often-cramped, frequently-changing headquarters of her company.  In 1990, strapped for funding, the Opera Company of Boston closed.  Caldwell later led the opera program at the University of Arkansas, until returning to New England several years ago.