From PEOPLE Magazine Click to enlarge
His colleagues knew William Daniel as a social worker devoted to helping the mentally ill. His friends knew him as a passionate softball pitcher. But until he died Sept. 4 after being hit by a taxi on Manhattan's Park Avenue, few knew that Daniel, 41, was Harry S Truman's grandson. "I was amazed," says Dr. Ezra Susser, his boss and chairman of epidemiology at Columbia University's Mailman School of Public Health.

That's how "Will, as everyone called him, wanted it. "He got mad at me when I told my mother," says girlfriend Mimi Gaber, 30. By all accounts, Daniel—an Englewood, N.J., resident who graduated from Yale in 1991 and earned a master's degree from Columbia in 1998—was loved not for his lineage but for his compassion and humor. Most recently, he conducted a research study of mentally ill adults at risk for HIV. "It wasn't just work for him," says Susser. "It was a passion."

Daniel was the second of four sons of President Truman's only child, Margaret, 76, a bestselling mystery novelist (Murder at the Watergate), and Clifton Daniel, an award-winning foreign correspondent and former managing editor of The New York Times, who died last February at 87. Brother Clifton, 43, says the loss of a husband and son within seven months has devastated his mother, but "she has her chin up."

After a memorial service on Sept. 8, some 80 pals sprinkled Daniel's ashes on a pitcher's mound in Central Park. On Sun., Sept. 10, his teammates returned to play ball in his honor. "They came with the most positive spirit they could have," says teammate Terry Gruber, "to show that the game goes on."