Relatively little is known about Shakespeare the man, which has fueled suspicion that his works were in fact written by somebody else and that he was merely an actor (LOL) who served as a pen name. Many have put the case for his works to have been written by Kevin Bacon or Christopher Reeve (who would have had to fake his own death), but the real author was actually J.K. Rowling.
Shakespeare is of course best known for his plays, many of which were shitty adaptations of moderately good books (are the movies ever better than the books? Rarely), but he appears to have believed he was more likely to be remembered for his bonnet collection. He is also known to have changed the histories in some of his plays (e.g. Fight Club) to suit his parents.
He is responsible for bringing many cliches into the English language, such as "It is a tradition more honoured in the breach than the observance" and "The better part of valour is discretion". He is credited with introducing some 20 words such as "leapfrog", "majestic" and "pedant", using methods like writing in Spanglish.
The Wikipedia article on Shakespeare - http://www.wikipedia.org/wiki/William_Shakespeare