When Idaliz Dolly Lenz walked into the restaurant, it seemed only natural to say to her: “Hello, Dolly!”

“Hello, hello – I’m sorry I’m late,” Ms. Lenz, who is executive vice president and managing director of Prudential Douglas Elliman, said. “I’m really sorry to be late. I always show up on time. I’m really sorry.”

The real estate executive wasn’t that late, but Ms. Lenz apologized through the subsequent photo shoot and stopped only when she sat down to order lentil soup and duck sausages.

It was obvious she was hungry – and no wonder: She had run her usual daily 10 miles in Central Park before dawn, seen her 16-year-old son, Joseph, and 15-year-old daughter, Jenny, off to school, said goodbye to her husband, Aaron, an accountant, and then had a series of meetings, which pushed into lunchtime.

That had been a typical morning for Dolly Lenz (no one ever calls her Idaliz, an amalgam of the first names of her two grandmothers). Her working days don’t end until 2 a.m., seven days a week, and they are packed with efforts to arrange sales of nearly $1 billion worth of condominiums, co-ops, and townhouses that are exclusively listed with her. In 2004, Ms. Lenz reportedly made nearly $7 million in commissions alone.

“I like to work all the time,” she said. “I can work 15 deals all at once, and every deal is compartmentalized in my mind. I have the best work ethic of anyone I know, and I have boundless energy. I am totally obsessed with making deals happen.”

This obsession doesn’t show on her face, which glows with good health. She has a particular aura that turns heads, and that, in Ms. Lenz’s case, proves distracting to nearby diners.

So it was especially startling when Ms. Lenz said, “I wasn’t always like this. I was obese.”

Obese? This slim woman in a black Akris dress, white Versace shirt with vintage Chanel pins, Yves St-Laurent glasses, and black Manolo Blahnik shoes? Surely she was joking.

“No joke,” Ms. Lenz said. “And it was a public humiliation that made me change my appearance.”

It happened this way: She was having lunch at the Harry Cipriani restaurant on Fifth Avenue with a real estate player, a man she’d long admired and who she thought also respected her.

“But it was clear that he was ignoring me throughout the lunch,” Ms. Lenz said. “Each time some slim, pretty woman came in, he’d stare. And if he knew her, he would gush all over her. But here I was, probably more successful than anyone in that room, and he was ignoring me because I was fat and frumpy.”

She paused, and then said: “I said to myself there and then that no one would ever, ever ignore me again.”

Ms. Lenz went on a low-carbohydrate diet, losing 23 pounds in the first month, and more than 60 pounds over an extended period. She started running every day, no matter what the weather.

“When I put my mind to something, I never let anything get in the way,” Ms. Lenz said. “I’m a big fighter. I’m a survivor.”

That kind of determination has been on display since the age of 12, when Idaliz Dolly Camino – the daughter of Manuel and Lucy Camino, both born in Spain – made sandwiches at a delicatessen in her Washington Heights neighborhood. She moved to a clerical job at Waldbaums, where she impressed her superiors with her ability to memorize the price of virtually every item in the store.

Then it was on to Baruch College, where Ms. Lenz studied accounting while working as a floor-area manager. After that, she obtained a master’s degree in auditing at the New School University. Macy’s offered to hire her permanently. But Ms. Lenz chose to join United Artists as an auditor.

“It was a boring job, but I became very good at figuring out how things work in the entertainment industry – I became very good at dismantling accounts and putting them back together.”

She also became very good at developing a network of entertainment personalities, some of whom would later become her clients and friends. Her husband encouraged her to go into real estate, so Dolly Lenz the accountant became Dolly Lenz the real estate businesswoman.

She concentrated on the high-end market. She became close friends with Barbra Streisand, who opened many doors for her. Her show business clients included Bruce Willis, Cameron Diaz, and Mariah Carey. Ms. Lenz has sold more than $4 billion worth of Manhattan apartments, including many in the new Time Warner complex.

Her fluency in English, French, Italian, Portuguese, Spanish, and a smattering of Arabic is an asset, especially with overseas clients. Another resource is her Rolodex, which includes contacts she cultivated over many months spent in East Asia wooing clients as part of a road show sponsored by Donald Trump.

She is quick to credit Mr. Trump and Howard Lorber – a legendary figure in real estate – as mentors. But she acknowledges that some say she’s competitive to a fault.

“I only compete with myself,” Ms. Lenz said. “I’m all about the true joy you feel when you get to do the thing you love the most – something that you love so much that you can’t stop. I’m very grateful to be where I am, which is why I always tell younger people who are entering this business: ‘Find your passion, then knock yourself out to fulfill your dreams.’ I tell them to develop long-term relationships. It’s always one foot at a time – you’ve just got to be the best you can every step of the way.”