Sue Ellen Cooper never meant to start a movement. In 1998, when she cajoled five friends to dress up in purple outfits and big red hats...

Sue Ellen Cooper never meant to start a movement.

In 1998, when she cajoled five friends to dress up in purple outfits and big red hats and head out for a few hours of silliness and fun, the Fullerton, Calif., wife and mother of two had nothing more in mind than a one-time break from her everyday routine and the chance to let down her hair and play.

“I’d been inspired by that famous poem,” says Cooper, 62. (The poem, titled “Warning,” by British author Jenny Joseph, begins, “When I am an old woman, I shall wear purple with a red hat that doesn’t go … .”) “So I got my friends to put on these outrageous outfits, and we all went out to tea, laughed and had a great time. And I thought that was the end of it.”

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But the outing was such a success that the group planned another, then another and another, until they were meeting regularly each month, always outfitted in scarlet hats and purple duds. After a magazine article featured tales of Cooper and friends meeting for tea dressed in red hats and purple clothes in July 2000, dozens of e-mails poured in asking, “What is the Red Hat Society and how can I join?” Six months later, The Orange County Register ran a story about the group that was picked up by a wire service and appeared in newspapers throughout the U.S. E-mails increased to hundreds, daily.

“I didn’t know where this was going,” Cooper says. “But I knew we would have fun getting there.”

She set up a “Hatquarters,” for what she refers to as a social “dis”-organization, dedicated to women’s friendships and having fun. In 2004, her first book, “The Red Hat Society: Friendship and Fun After Fifty,” was published. Within days, it shot to No. 3 on The New York Times best-seller list. Her second best-seller, “The Red Hat Society’s Laugh Lines: Stories of Inspiration and ‘Hattitude,’ ” was released in 2005.

These days, Cooper, better known to her loyal and adoring subjects as the “Exalted Queen Mother,” reigns over close to 1 million “women of a certain age.” (Red Hat Society members range in age from 50 to over 100.) Since its inception, the Red Hat Society has grown to include nearly 40,000 chapters — with such names as “The Scarlet O’Hatters,” “Beguiling Red Hat Biddies” and the “Beary Hot Hatters” — in all 50 states and 30 countries. A new membership segment, Pink Hatters, is made up of women younger than 50 who wear pink and lavender.

“Younger women were jealous of all the fun we were having,” Cooper says. “When ‘Pinkies’ turn 50, chapters hold ‘hat-uation’ parties.”

Over the years, the group has established itself firmly in the public consciousness. Regional and national conventions draw thousands. Organized trips and cruises draw hordes of red-hatted “girls” who wanna have fun. “The Red Hat Society Cookbook” was published in 2006, and “Eat Dessert First: The Red Hat Society Dessert Cookbook” is due in stores in September. A series of Red Hat Society romance novels has a wide audience. A documentary film, “The Remarkable Red Hat Society,” debuted on PBS earlier this year. An exercise program developed with AARP, “Step & Stride with Ruby,” helps keep Red Hatters in fine form. Licensed Red Hat merchandise includes hats, clothing, jewelry, hat racks, ruby slippers and even Red Hat cookies, candies and cakes.

Several years ago, a producer approached Cooper with an idea for a musical based on the group’s philosophy. The result, “Hats!” with songs by Grammy winner Melissa Manchester, Amanda McBroom and Pam Tillis, debuted in Denver last year, recently completed a run in Chicago and will be touring in 2008.

In spite of the group’s higher profile, fun is still the No. 1 priority, Cooper says. It will be celebrating its 10th anniversary in 2008 with a year of festivities, frivolity and friendship.

“We stay away from politics and religion,” Cooper says. “If people insist on bringing up those topics, we plug our ears and hum until they stop. We’re still all about celebrating women’s friendships and nurturing ourselves and each other.”