PAUL Samuelson, called the 'foremost academic economist of the 20th century,' was an inescapable presence in our young, Third World lives. The reason? His textbooks, of course, on introductory economics, which had — and still have — global reach. Plus, the exacting and rigorous mathematical grounding of his economic writings and theorizing, for which he won a John Bates Clark medal and the National Science Award. Samuelson was also the first American economist to win the Nobel Prize in economics. In between his ultra-serious work, Samuelson found time for some economic humor. 'GDP falls when a man marries his maid,' he once wrote.