Britain's Queen Elizabeth II is a public-private monarch.

Britain's Queen Elizabeth II talks with officers at an event with the Argyll and Sutherland Highlanders, 5th Battalion, the Royal Regiment of Scotland in London on May 30, 2012. The queen keeps a busy schedule of public appearances. (Lewis Whyld / AFP/Getty Images / May 30, 2012)

LONDON — Her face is everywhere: on stamps, coins, mugs and book covers. Her likeness has just been reproduced for the 23rd time at Madame Tussauds, London's famous wax museum. More visitors come to gawp at her house than probably any other residence in the world.

Yet after reigning over Britain for longer than most of her subjects have been alive, Queen Elizabeth II is the country's "most familiar enigma," in the words of one TV presenter.

Yes, the white-haired 86-year-old keeps up a grueling schedule of public appearances that would test someone half her age, especially during this season of celebration of her Diamond Jubilee, marking 60 years on the throne. This weekend, the queen kicks off a four-day extravaganza by going to the races Saturday and cruising down the Thames on Sunday at the head of a flotilla of up to 1,000 boats.

Photos: Queen Elizabeth II through the years

But a certain regal aloofness, a touch of otherworldliness that lends some credence to the title "Your Majesty," is a crucial component of her long success as monarch, some say.

"You do need a little bit of mystique," said Sue Daws, 52, who lives in northern Wales.

Note to heirs: You might want to work on that.

Elizabeth is the last member of the House of Windsor for whom royalty and celebrity don't overlap, or at least not by much, a distinction many observers credit with helping to preserve the monarchy's appeal.

Her discretion and dignity are in marked contrast to the behavior of her four children. Unlike them, she doesn't submit to tell-all interviews about unhappy marriages, hasn't had details of her sex life laid bare in the tabloids, didn't take part (not even for charity) in an embarrassing game show called "The Grand Knockout" in 1987 (as did Princess Anne and Princes Andrew and Edward, in a moment that for many Britons represented "the breaking of royalty's magic spell," as one writer later put it).

Just last month, viewers of the BBC in Scotland switched on the TV to find their future king, Prince Charles, giving the daily weather report in his immaculately clipped tones, a surprise appearance that's become a minor hit on YouTube. ("Potential for a few flurries over Balmoral [Castle]," he said of his family's Scottish quarters, then stopped and asked, "Who the hell wrote this script?")

Although it was a good-natured and generally well-received cameo, a spot of hammy humor from an often stuffy heir apparent, no one can possibly imagine the woman he calls "Mama" doing the same thing.

"The queen has always avoided what she calls stunts," said Robert Lacey, author of the just-published "The Queen: A Life in Brief." "The monarchy has got to distinguish itself from other aspects of British public life."

Part of Elizabeth's aura of solemn reserve is natural to her temperament and her generation, with its harrowing experience of world war and its innate aversion to making a spectacle. Lacey notes that she grew up in the era depicted in the movie "The King's Speech" — the king in question was her father — when mass media were still novelties and engaging them wasn't automatically part of the British sovereign's job description.

But some of the queen's detached grandeur is carefully cultivated and maintained.

There are countless biographies, but no autobiography. Her public comments are polite, unexceptionable and totally unrevealing. Everyone knows about her love of dogs and horses, but only those closest to her have any real inkling of the thoughts beneath the diamond tiaras and behind the guarded smile.

"She is the most portrayed individual in history, more than anyone you can think of — popes, prime ministers, presidents," said Paul Moorhouse, curator of a new exhibition, "The Queen: Art & Image," at the National Portrait Gallery here in London. "The paradox is, what does anyone know about her? Her opinions are a closed book. Nobody but her intimate family knows what she thinks."

Royal protocol certainly helps perpetuate the idea of a person set above and apart. At meals, guests are supposed to stop eating when the queen does. (It's said she keeps a final morsel on her plate to roll around so that others can keep noshing without embarrassment.) Even her family members have to rise when she enters.

"Whenever Granny walks into a room, everyone stands up, stops and just kind of watches her," her granddaughter Princess Eugenie told the BBC recently.

"I find that incredible. I kind of go, 'Ah,'" Eugenie said, feigning a gasp.