Inside the world of the modern-day butler

FORTUNE — When Allan Miller started as a butler 25 years ago he had no idea what he was getting into. Now, when he talks to students about his career as a butler or estate manager, they have no idea his job even exists.

Yet thousands of butlers work at private homes, resorts, and in consulting roles that look only a little like those portrayed in the television show Downton Abbey or period movies such as Gosford Park. Instead of polishing silver or greeting guests, the butler may oversee installation of a new heating system or pay all the household bills.

Or if a butler works in a hotel, he or she may fetch a favorite brand of beer or a pair of cufflinks, pack suitcases, and hang banners for guests. “Whatever it is, we can get it for them,” says Ike Podlesny, a butler at The Lodge at Sea Island in Georgia. “As long as it’s not illegal or immoral, we’ll get it done.”

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Podlesny and the nine other butlers at the resort have helped with wedding proposals, on the golf greens and off, and serve room service food so that it seems like it’s in a fine restaurant. They greet guests by name, track down lost luggage, and serve as a sort of personal assistant.

Butlers also cater to well-heeled guests at Ritz-Carlton and many other luxury hotels. But, like Mr. Carson on Downton Abbey, they’re best known for their work overseeing private households of the very rich. There they may manage a raft of contractors keeping up gardens, pools and all kinds of heating and security systems, and orchestrate parties and events.

Many today favor a broader title — household manager or estate manager — that fits into a field called private service, working in mansions and homes that are 10 to 15 times the size of average American abodes.

“People still think of butler as a very stuffy position, even though it’s not. We have some people calling it majordomo,” a male domestic, says Susan Joy Feigon, a principal with Feigon Hamilton, which places professional household staff in positions. The job can vary quite a bit, depending on the family, how many homes they have, what their lifestyle is like, and whether they employ a chief of staff, family office manager, or director of residences — all of whom tend to oversee everything, including the butler.

Striving for invisibility?

Alan Miller, 51, started as a butler by accident after owning a small barbecue restaurant. “I got a call from Atlanta, a gentleman named Will,” he recalls. His future boss had contracted polio in college and was paralyzed from the neck down, but also very successful in business. “He said, ‘you’re going to learn from the people you work for, learn about goal setting … time management, money management,’ ” Miller says.

He quickly learned that the job required the ability to handle many projects simultaneously. “The job is much more intense in terms of multitasking and smart technologies,” says Miller, who lives near Seattle and still considers himself an old-school butler.

“In the corporate world you strive for recognition. In the private service world, your goal is invisibility,” he says. “When things are going very, very smoothly and they don’t notice you, then you’re successful.”

Successful butlers can earn handsome salaries, plus as much as a month’s paid vacation and a 401(k) plan. Top household managers can earn up to $300,000 a year, says Feigon.  Several jobs posted recently paid $200,000 to $250,000 in Boston and near San Francisco. At those pay grades the job likely includes managing a sizable staff and dozens of contractors.

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The butler is also expected to stay abreast of the latest software and security systems. “Homes are so complex, estates are so large, with wine cellars, smart home technologies, and security screens,” not to mention all kinds of commercial equipment in kitchens and laundries, says Miller. Butlers handle all the unpredictable needs of the household, while housekeepers manage the predictable ones such as cleaning rooms.

The new face of today’s butler

Though butlers in period dramas are all male and somewhat older, today women are working in the field, as are younger men. What’s most important is that the butler “needs to mesh with the family,” explains Gail Hamilton, Feigon’s business partner. Besides using placement agencies, some wealthy families require butlers and other key household staff to take personality tests, she says.

To land a new assignment, many butlers work with placement firms. Many become butlers after they outgrow another job as a personal chef or a nanny, Feigon says. Some attend one of a handful of “schools” or institutes that offer training, or they may learn on the job.

Demand for butlers increased during the tech boom of the late 1990s, she says. Feigon sees continued growth in the field, driven by gains in wealth. And many luxury hotels have added butlers to their ranks in recent years.

But others claim that opportunities for butlers are scarcer than they have been in the past. The number of butlers and estate or household managers working in the U.S. has declined, says Matt Haack, founder and president of the Domestic Estate Managers Association, who bases his estimates on conversations he’s had with placement agencies, working butlers, and his members, individuals who work in the field. Even wealthy families have consolidated and combined some jobs in a tighter economy, he says, adding that Downton Abbey has spurred “an influx of information requests about butlers.”

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Miller thinks some newly wealthy individuals do not understand the need for professional help managing their property and their lives. A talented butler used to be able to contact his agent and within days, decide on a position to pursue. “Today, it’s not so. I’ve seen some very qualified people wait for months and months for even an interview, let alone an offer,” says Miller, who’s starting to plan a second career.

It’s clear that the butler’s world is evolving, so that more and more, they will work in hotels and for companies as a sort of concierge. Lisandro Lozano Aguiar worked in hotel security before becoming a butler at Villa Premiere Hotel & Spa in Puerto Vallarta, Mexico. He had to learn English and spent two weeks at a hotel training school in Mexico City. At first, ironing garments for guests “was a little bit kind of hard for me,” he says. After seven years as a butler, he has mastered that skill, as well as locating the right book for a guest, choosing a flower arrangement for birthdays and anniversaries, and creating a rose petal-covered bed for honeymooners. “We are ahead of our guests’ needs. We like to be there before they ask.”