When Mary Tonry met Louis Theodore at a Queens bar in 1963, she thought he was “a lot of fun — but nothing serious.”

Things can change — especially impressions.

“He wined and dined me, took me to clubs like the Copacabana,” she recalled recently. Then one day, Mary visited Lou while he was with his students at Manhattan College. “He was just a little older than they were, but you could tell they were very excited to work with him,” she said. “I saw another side of him. I was surprised — and pleased.”

Mary, 75, who became Mrs. Theodore 50 years ago, said she continues to see different sides of her husband’s multifaceted life — from book writing to keeping an active social life, to fanning his passion for basketball, to playing chess with his grandsons.

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Having such a varied approach to life, experts say, should be a model for aging adults. While researchers generally agree that several factors — especially regular exercise and a healthy diet — contribute to longevity, there is growing evidence that “being vitally engaged is important to a long life,” said Tobi Abramson, a Hewlett-based gerontologist and director of geriatric mental health for the New York City Department of Aging. “When you’re engaging in activity that gives life purpose, you build up the resiliency to go forward.”

Theodore retired from teaching chemical engineering years ago but continues to work on various projects from home in East Williston. At age 83, he is still consulting, presenting papers at conferences, and writing texts and reference books. Currently, he’s collaborating on five books in various stages of completion — adding to the 108 he’s written or co-authored so far. His take on juggling multiple new books? “I’m slowing down,” he said.

Maintaining close ties with colleagues, former students and basketball players he’s coached over the years is a source of pride. “I value them,” Theodore said. “They’re memories I don’t want to forget. They’re still an integral part of my life.”

Active life

Theodore’s social facility is not lost on his family. “He finds a way for professional and personal things to go together,” said daughter Molleen Theodore, 45, associate curator of programs at the Yale University Art Gallery. “His friendships are long-standing, and he’s always making new ones.”

For Theodore, staying engaged also means keeping a hand in his lifelong love of basketball by supporting youth sports leagues and attending Hofstra University men’s basketball home games, where he seats himself at the media table. He writes occasional opinion columns about the team and other subjects for a weekly newspaper. Two years ago, he published his first nontechnical book, “Basketball Coaching 101,” an eclectic compendium of personal stories and a spray of tips and commentary from coaches, players, officials, journalists and fans.

Writing on basketball — a subject far afield from his other tomes — was a challenge — one he tackled with considerable trepidation, Theodore said. But in doing so, he was taking his own advice: “I tell young kids, ‘If you want to be successful, you need to accept that you’re going to fail sometimes,’ ” he said. “Failure is OK; it’s part of life.” As a neophyte professor, he recalled, his first 19 research grant proposals were rejected. “It hurt,” he said. “But the 20th time, it hit.”

Theodore spent his early years in Manhattan’s Hell Kitchen, where his father, George, owned a small luncheonette. “I fell in love with basketball the first time I touched one,” he recalled in his coaching book. “It was at a play session in a gym following a Boy Scouts meeting sometime around 1945. Perhaps it was the team play, or the need to encourage each other, or no ridiculing each other, or not bullying one another, or simply the thrill of throwing a ball through a hoop, or all of the above.”

The family moved to Astoria in 1955 and Theodore, who recognized he had “limited basketball ability” (he’s 5-foot-6), went on to earn a bachelor of science in chemical engineering at Cooper Union and a Ph.D. at New York University. But his love for basketball did not diminish. While in graduate school, he persuaded the owner of Killeen’s Tavern in Astoria to sponsor a team, and Theodore began recruiting local kids, many of whom played for their college teams, to play for Killeen’s during the summer. He was in charge of the team.

“Lou was a good coach,” said Danny Doyle, 77, a member of the Killeen’s team who played briefly for the Detroit Pistons, then in the Eastern League. “He’s an intelligent guy; he did a good job. Anybody who was good wanted to play with us.” Doyle, now a North Merrick resident, played for Theodore’s teams through the early 1960s. They won several tournaments and some members later played professionally in the National Basketball Association and on minor league teams, and others went on to successful coaching careers. Doyle and Theodore co-owned the tavern for a few years and they remain close friends.

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Theodore was also a mentor to students at the university. One of them became a collaborator on Theodore’s books. Frank Ricci, of upstate Mount Kisco, got a bachelor of science degree in chemical engineering from Manhattan College in 2010 and is now a senior scientist in the Danbury, Connecticut, office of pharmaceutical giant Boehringer Ingelheim, in addition to teaching at Manhattan College. He met Theodore in his freshman year.

“Lou popped in to check out the summer lab,” Ricci recalled. “I knew who he was and said, ‘How are you doing, Dr. Theodore?’ He said, ‘None of your business’— his trademark sarcasm,” Ricci said. “I knew right then we were going to get along well.”

Over the next couple of years, Theodore asked Ricci to co-author two technical books with him, an extraordinary opportunity for an undergraduate student. “He took a shot on me. He altered the trajectory of my life.” Ricci said he often calls his old professor for advice.

Wide range of books

During Theodore’s 55 years at Manhattan College, he became director of the chemical engineering graduate program and was a widely recognized authority on environmental management. His books cover an expansive range of topics, including environmental ethics, air pollution control equipment and nanotechnology. Filled with technical analysis, they are also sprinkled with references that hint at Theodore’s intellectual curiosity. For instance, in a 600-plus-page tome, “Environmental Health and Hazard Risk Assessment/Principles and Calculations,” Theodore weaves a history of environmental accidents with chapters on emergency planning procedures in response to terrorist attacks, probability simulations, and even quotes from historic literary figures, such as Cervantes and Voltaire.

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When his three children were younger (his oldest, Georgeen, 48, of Brooklyn, is an architect and urban designer; his youngest, Patrick, 42, of East Williston, is a New York City police detective) he would bring them to industry conferences, blending educational and recreational time.

“He worked really hard, but he also instilled in his family the importance of taking vacations,” said daughter Molleen. Every year the family would go to Saratoga during racing season and to the beach. “He likes to sit right at the water’s edge and read and work,” Molleen said. “That’s where he feels happiest. . . . Not at some quiet and pristine beach, but Field 6 at Jones Beach. He has this real ability to work around noise and chaos.”

Theodore continues to challenge himself with the usual puzzles and word games. He also is pondering a second edition of his basketball book.

“I want to have things to do,” Theodore said. “I need that.” Down the road, he has yet another plan: To write a book with a 9-year-old grandson, Julian, who is one of Theodore’s new chess opponents. “He’s a math whiz,” Theodore said. “I told him, ‘When you’re 17, I’m going to write a math book with you.’ I don’t know what it’s about yet, but we’re going to write it.”