George Edward Moore, Philosopher. (1873-1958)
One of the most famous philosophers of the last century. He was one of the primary founders and supporters of analytic philosophy. He is most famous for his attacks on metaphysics, his common sense realism, and the naturalistic fallacy.
Common sense Realism, in his case, was the belief that what you 'know' is real is, in fact, real. He claimed that he knew with absolute certainty that he had a living body, that there were other living bodies, that space and time existed in exactly the sense in which they are usually used, etc. As you can see, he is using 'common sense' to mean something that most (if not all) people are certain of. His main defense of these propositions was simply that he is certain that they are true. This is usually considered a poor proof by other philosophers.
The reason he bothered to mention that all of these apparently obvious things were true was because there were many metaphysisits (Josiah Royce, Francis Bradley, John McTaggart {See absolute idealism}) who made their living doubting them. The charitable interpretation of Moore is that he is pointing out that while his common sense propositions things may not be certain in the strongest possible sense, any argument that claims one of them to be false will have to assume something that is less certain.
You don't want to read Moore. Most of his stuff (from my admittedly limited readings) is painful if not impossible to read. I have read one chapter from his book Principia Ethica, and it was readable and worthwhile (although completely wrong).
He has one famous pseudo-quote that any student of philosophy will recognize:
Here is a hand, (Motions with hand)
And here is another (Motions with other hand)
Therefore, Idealism is false.