Glen B. Nelson’s commitment to hard work in the business world was matched only by his dedication to family.

Nelson, CEO and founder of Matrix Realty Group — a multimillion-dollar real estate investment and management company with commercial and residential properties across the country — died Dec. 20. He was 48.

Nelson, of Port Jefferson, died of a heart attack, which caused a single-car accident, family members said. He was pronounced dead at St. Charles Hospital in Port Jefferson, they said.

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Christopher Nelson, 21, of Port Jefferson, said his father emphasized morals to his children in business and in life.

“He was very loving . . . He believed in doing the right thing for other people,” Nelson said. “I’d be extremely proud if one day I could be half the man that he was.”

Born in Queens as the middle child of four siblings to parents Kenneth and Rosemarie Nelson, Nelson was always driven, said his ex-wife Sandy Nelson, who met him when they were teenagers. At age 16, he worked two jobs — as a school janitor and restaurant dishwasher, she said.

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Nelson graduated from Ward Melville High School in East Setauket in 1984, and took classes at Suffolk County Community College, said Sandy Nelson, 48, of Port Jefferson Station. He received his stockbroker’s license in 1987, but left the industry to work as a broker for a coin company based in Port Jefferson, she said. The two married in 1988, had four children and divorced about 15 years later, she said.

In 1989, Nelson started his own coin business. By 1993, he had earned enough capital to purchase his first commercial building at an auction, Sandy Nelson said. It was the official start of Matrix Realty Group.

“I’ve never met anyone like him that had that much drive and tenacity. ‘No’ was never an option for him,” she said. “I think his humble beginnings motivated him.”

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Nelson built his business by acquiring undervalued properties, upgrading and leasing them to tenants and then selling the properties at key market times, family said. With his profits, Nelson acquired larger buildings. Matrix currently has a portfolio of more than 3 million square feet of commercial office space and more than 7,000 units of multifamily housing, said Gerard McCreight, the company’s chief legal officer.

“We lost our visionary, and we lost our leader, and we lost our friend,” McCreight said of Nelson. “We’ll keep Glen’s work ethic and spirit in our minds and hearts at all times.”

Susan Holsan, 49, Nelson’s fiancee and partner for more than a decade, said he enjoyed decompressing by traveling across the world, boating, and riding one of his three Harley-Davidson motorcycles.

“He was just a very good-hearted, old-school man,” she said, adding that he treated her 20-year-old son Mitchell Holsan as his own. “He helped so many people. He was very humble.”

Nelson’s daughter, Brianna Nelson, 25, of Port Jefferson, said her father made his mark on the world.

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“He was a true leader who was able to motivate people to see his vision and execute it,” she said. “He really believed that God was looking out for him because he worked so hard . . . He always said that if you work hard, there are no limitations.”

Nelson’s youngest daughter Gina Nelson, 19, of Port Jefferson, recalled talking and laughing with her father for hours. Family trips to Italy, the Bahamas and the Dominican Republic were cherished memories, she said.

“It was like he relived his childhood through watching us, because he didn’t have anything remotely close to what he was able to give us,” she said, adding that he also stressed humility. “He was just a rock in the family. He was my favorite hello and now, he’s my hardest goodbye.”

Nelson is also survived by another son, Phillip Nelson, 23, of Port Jefferson; brothers Kenneth Nelson, of Rocky Point, and Jeffrey Nelson, of Coram; and a grandson. He was predeceased by sister Michele Rosario and brother Troy Nelson, both of Coram.

A wake and funeral were held last month, followed by burial at Washington Memorial Park in Mount Sinai.