Paul Erdos

He would appear on the doorstep of fellow mathematicians without warning--a frail, disheveled, elderly man, hopped up on amphetamines and wearing a ratty raincoat--and announce, in a thick Hungarian accent, "My mind is open." For a day, or a week or a month, the man or woman who answered the knock would have to take nonstop care of this helpless guest who couldn't figure out how to cut a grapefruit or wash his underwear--and in return would be permitted the exhausting, exhilarating experience of following the thought processes of Paul Erdos, the most prolific and arguably the cleverest mathematician of the century.

In a profession with no shortage of oddballs, he was the strangest. Erdos had no home, no possessions and no life aside from mathematics. He spoke a language all his own: "died" meant someone had stopped doing math; "left" meant the person had died; God was the "Supreme Fascist."

He was as generous as he was brilliant. Instead of hoarding his ideas, he shared them with all comers. Indeed, as many as half a dozen mathematicians would sometimes gather to wrestle with Erdos' provocative notions about integers, whole numbers and primes--furiously scribbling complex proofs as the old man flitted among them, imparting astonishingly acute insights in wholesale lots.

By the time he "left" at the age of 83, in 1996, Erdos had collaborated with an unprecedented 485 colleagues. Other mathematicians simply solved problems; Erdos solved problems and pushed at least four generations to dig deeper into the mysterious nature of numbers.