Like many mathematicians, Paul Erdos was famously eccentric. He had no interest in money, giving his meager earnings to strangers, beggars and promising young students. He had no family, job or hobbies, dedicating his life entirely to mathematics. Most incredibly, he never had a fixed address. Rather than purchase a home of his own, he had a network of friends all over the world with whom he could stay. He would simply drop in (unannounced) with his two battered suitcases, and say: "My brain is open." His motto? "Another roof, another proof!"
[Erdos was in the habit of calling colleagues all over the whole world, irrespective of the local time. While he easily remembered their numbers, however, he remembered very few first names. Among the few people who were called by their Christian names was Tom Trotter -- whom Erdos called Bill!]