Assistant Allison Borio says Mrs. Reagan died Sunday at her home of congestive heart failure.
Her marriage to Ronald Reagan lasted 52 years until his death in 2004.
A former actress, she was Reagan’s closest adviser and fierce protector on his journey from actor to governor of California to president of the United States.
She rushed to his side after he was shot in 1981 by a would-be assassin, and later endured his nearly decade-long battle with Alzheimer’s disease. In recent years she broke with fellow Republicans in backing stem cell research as a way to possibly find a cure for Alzheimer’s.