"She was a wife, a mother, a grandmother, a friend, a mental health advocate and a cultural icon," the agent's statement said. "She will be greatly missed."
When Duke was 12, she starred as Helen Keller in the Broadway play The Miracle Worker. She reprised her role in the 1962 film version, winning an Academy Award for best supporting actress when she was 16 — then the youngest person to have won an Oscar.
In 1963, Duke took the starring roles in a popular sitcom called The Patty Duke Show,in which she played identical cousins. NPR reported that she was the youngest actress in television to have a prime-time series built around her.
The Los Angeles Times notes that "after her successful stint as Patty and Cathy Lane on television, Duke tried to transition back to film with a controversial performance as Neely O'Hara in 'Valley of the Dolls,' in which the actress portrayed an alcoholic, drug-addled star."
But Duke's outward success belied her private struggles.
"The success ... masked personal misery which included depressions that led to suicide attempts and a string of failed marriages," NPR reported in 2000.
Diagnosed with bipolar disorder in 1982, Duke devoted her later years to championing mental health programs and raising her three sons, two of whom — Sean and Mackenzie Astin — followed in their mother's footsteps and became actors as well.
"I love you Mom," Sean Astin, who played Samwise Gamgee in "The Lord of the Rings" trilogy, said in a statement confirming his mother's death.
Duke, whose real name was Anna Pearce, wrote an autobiography in 1987 titled Call Me Anna that addressed some of these struggles.
Mandalit says Duke served as president of the Screen Actors Guild in the 1980s and adds: "After she was diagnosed with bipolar disorder, she became an advocate for mental health issues."
Mandalit says Duke served as president of the Screen Actors Guild in the 1980s and adds: "After she was diagnosed with bipolar disorder, she became an advocate for mental health issues."
After "The Patty Duke Show" was cancelled, Duke starred in the camp classic "Valley of the Dolls." She won a second Emmy for her turn in the 1970 Civil Rights drama "My Sweet Charlie" and a third in 1976 for her part in the TV mini-series "Captains and the Kings." She also appeared in a variety of TV shows ranging from Police Story and Hawaii 5-O to Night Gallery...