Born in Far Rockaway, New York, he is the author of many books on recreational mathematics, recreational logic, etc. Most notably, one is titled What is the name of this book?. It would hardly be considered a spoiler to reveal that the name of the book is, What is the name of this book?.
Many of his logic problems are extensions of classic puzzles. Those involving knights (who always tell the truth) and knaves (who always lie) are based on the story of the two doors & two guards, one who lies and one who doesn't. In more complex puzzles, he introduces characters who may lie or tell the truth, and furthermore instead of answering "yes" or "no", use words which mean "yes" or "no" interchangeably depending on which type of person they are. In his Transylvania puzzles, half of the inhabitants are insane, and believe only false things, whereas the other half are sane and believe only true things. In addition, humans always tell the truth, and vampires always lie. For example, an insane vampire will believe a false thing (2 + 2 is not 4) but will then lie about it, and say that it is. A sane vampire knows 2 + 2 is 4, but will lie and say it isn't. And mutatis mutandis for humans.
Popularizations:
Not all of Smullyan's writings are popularizations:
wikipedia.org dumped 2003-03-17 with terodump