[Michael] Bloomberg's father was a bookkeeper for a dairy who died of heart failure in 1963. After his death, Bloomberg's mother, Charlotte, went to work as a secretary. His parents were never all that consumed with material success, he says, adding that his 92-year-old mother has refused his offers to treat her to a nicer home, preferring to stay in the family split-level in Medford that Bloomberg's parents bought for $11,000 some 50 years ago. Mom, in fact, is still so independent that when she uses a car service at night that's billed to her son, "she sends me a check!" the billionaire says with incredulity. "It drives me crazy."