For a country that likes to think of itself as a land of opportunity and a place where equality reigns, America has long lagged behind an astonishing (one could even say an embarrassing) number of other nations in one elemental respect: electing a woman to lead. Ireland, Germany, India, Pakistan, Israel, England, Bolivia, Malta, Thailand, Australia and on and on—over the past century, more countries around the world have had women presidents and prime ministers than there are American states.
The U.S., meanwhile, for those keeping score, has had none. Nada. Zilch.
When it comes to female leaders at the highest level of government, however, what America has had is an awful lot of First Ladies—and it would be a reckless sort of denial to suggest that none of them wielded power, either behind closed doors or in the wider world beyond the White House. They might not have been elected heads of state, but the wives of the men who have occupied the Oval Office have, to a greater or lesser extent, exercised their own brand of command.
Classically “strong” women like Eleanor Roosevelt and Hillary Rodham Clinton, of course, embraced their public roles—before, during and after their husbands’ times in office—with a readiness and skill that marked them as formidable figures in their own right. Other First Ladies might have shown a more traditional, “wifely” demeanor to the world, but the quieter sort of strength that so many of them displayed as the better halves of the most powerful men in the world, in the glare of the media spotlight and often in the midst of genuine crisis, speaks volumes about the caliber of the couples who have lived at 1600 Pennsylvania Avenue.
Here, LIFE.com looks back at America’s First Ladies across six decades of the 20th century with a glimpse—through classic photos, as well as pictures that never ran in LIFE—into the public and private lives of the members of an uncommonly exclusive club, before, during and after their years in the White House.
Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter at @LizabethRonk.