As the Manhattan district attorney for 35 years, Robert M. Morgenthau has been, in the words of a former assistant, “a force of nature.” He has been a savvy and tenacious crusader against street crime and corporate greed who also is unafraid to take on corporate competitors.

At age 90, he moves slowly but he has never lost his zest for a job in which he has built up unparalleled influence over the criminal justice system.