Former U.S. first lady Rosalynn Carter, who President Jimmy Carter called "an extension of myself" owing to her prominent role in his administration even as she tirelessly promoted the cause of mental health, died on Sunday at age 96, the Carter Center said.

Rosalynn Carter, who in recent days had entered hospice care at home in Plains, Georgia, died with her family by her side, according to a statement released by the nonprofit organization founded by the couple.

Jimmy Carter, a Democrat, served as president from 1977 to 1981. He and his wife were the longest-married U.S. presidential couple, having wed in 1946 when he was 21 and she was 18. After his single term as president ended, he has also enjoyed more post-White House years than any president before him, and she played an instrumental role during those years, including as part of the Carter Center and the Habitat for Humanity charity.