Shirley MacLaine was just 21 when, with her film debut in Hitchcock's 1955 black comedy, The Trouble With Harry, she earned her first movie-acting accolades, including a Golden Globe as the female "New Star of the Year." In the six-plus decades since then, she's won an Oscar (for Terms of Endearment), more Golden Globes, two BAFTAs, an Emmy, an AFI Lifetime Achievement Award and, in 2013, was honored at the Kennedy Center for her indelible, lifelong contributions to the arts.
She's written numerous best-selling books; remains an advocate for civil rights, women's rights and social justice; and each week on her Independent Expression Radio show she (in the words of her official website) "interviews a new guest on topics ranging from politics, to UFO sightings, to the environment, and more."
Today, at 80 -- she was born April 24, 1934, in Virginia; her younger brother is Warren Beatty -- MacLaine is still performing (Downton Abbey, The Secret Life of Walter Mitty, Glee) and shows little sign of slowing down. Then again, in light of the life she's led offscreen, slowing down doesn't really seem to be in her nature. For example, she was married to businessman Steve Parker -- with whom she had a daughter, Sachi -- for almost 30 years, but as theirs was an open relationship, MacLaine was free to pursue, and be pursued by, some of the biggest stars of the 20th century. She counts among her many love affairs Hollywood rebel Robert Mitchum; Rat Pack founder and epic carouser Dean Martin; the French actor and singer Yves Montand; and even international political figures like former Canadian Prime Minister Pierre Trudeau and Olof Palme, the Swedish Prime Minister who was assassinated in 1986.
Here, on her 80th birthday, LIFE.com pays tribute to the one and only Shirley MacLaine with a series of classic photos highlighting her extraordinary -- and still-thriving -- career, and the charming combination of naïveté and carnality that have defined her appeal for so many, for so long.