Paul Erd?s was a mathematician. In addition to authoring significant papers himself, he created a series of Erd?s problems in which he offered (often small) cash prizes for solutions to difficult and/or significant mathematical challenges. He also had a great affinity for amphetamines, lived out of a suitcase, and drank endless coffee. This combo of genius, substance abuse, and intentional homelessness creates a pretty colorful character.
The hour-long documentary N Is a Number (shown below in its entirety) introduces Erd?s, following him in the years before his death. It also helpfully explains how to pronounce "Erd?s." If you have an interest in math, genius, or eccentricity, this is well worth your time.
A representative line from the film, spoken by Erd?s as he concludes a conference: "The only good wish for an old man is an easy cure of the incurable disease of life. The meeting, like life will, is nearing its end. But just like life, it was very pleasant."
Erd?s is so prolific that Wikipedia has a List of things named after Paul Erd?s. And, for the record, that's not an umlaut in his name -- it's a pair of long accents. Many publications just fall back to an umlaut because that's all they've got. But we've got coffee and proper typography, people.
See also: Bacon numbers, which are basically the same as Erd?s numbers.