The 63-year-old has never married and never had children, but the children were very important to him. He encouraged some children and took care of his brother, Daniel, who had developmental disabilities.
Naiman became a social worker after he left a banking career.
"He was a valuable employee who was trustworthy and committed to his work," said Deborah Johnson, a spokeswoman for Washington's Department of Education, Children, Young People and Families.
He worked three jobs to establish in the new field, said Shashi Karan's friend on CNN.
Karan and Naiman collaborated with the bank in the 1980s and kept contact for decades until his death on January 8, 2018.
"It was just this guy who could not just spend the money. It was just in his nature to save the money and put it aside," Karan said.
Karan said he was one of the few people who knew how much money Naaman had.
"I think he always knew he would leave his money for charity," said Karan.
Friends had talked about investments and savings over the years, and when it was time for Naiman to make a will, he asked Karan to be his executor.
He said that Naiman had a remarkable heritage when his father died, who added to his fortune.
Hunting, saving and tackling hunting is more like a hobby for Naiman than a sacrifice.
"Saving money was a kind of game for him," said Karan. "He would be happy about how he had a whole day out and did not have to spend a cent."
Naiman loved the cars and when his brother died in 2013 he made a rare mess of himself and bought a Scion FR-S sports car.
"It's a nice little sports car, but it's not a Mustang or a Corvette or a Porsche that could easily be offered," Karan said.
Naiman thought he was traveling more or buying a house with a nice view, but his cancer cuts off these plans.
Karan said that after his diagnosis, Naiman spent much time researching charity organizations.
A team that benefited from its kindness is the Paediatrics Care Center, which caters for medically fragile babies suffering from exposure to pre-natal medicine.
"We are so grateful to Alan, not only for his legacy but also for the life he has devoted to children," the team wrote.
Karan said the donations came mainly from children's charities, such as Make-A-Wish, Boys Town, and Flanagan's Treehouse, a nonprofit center that helps children underwrite. He also gave money to the Catholic Church of his parents and to American veterans with special needs.
Naaman was excited to think how well his money would be when the time came, said Karan.
"My gift will be larger than their annual budget and will remove them," recalls Karan. "And he did."