George Edward "G. E." Moore OM, FBA was philosopher, one of the founders of the analytic tradition along with Bertrand Russell, Ludwig Wittgenstein, and (before them) Gottlob Frege. With Russell, he led the turn away from idealism in British philosophy, and became well known for his advocacy of common sense concepts, his contributions to ethics, epistemology, and metaphysics, and "his exceptional personality and moral character." He was Professor of Philosophy at the University of Cambridge, highly influential among (though not a member of) the Bloomsbury Group, and the editor of the influential journal Mind. He was elected a fellow of the British Academy in 1918. He was a member of the Cambridge Apostles, the intellectual secret society, from 1894, and the Cambridge University Moral Sciences Club.
Idealism in the philosophical context is such a mindf*ck and G.E. Moore's refutation of it is even more of one. That makes it very interesting and quite wild.
A pro-tip though: if you want his detailed argument and supposed proof against idealism wherein he suggests the Idealist way of arguing for the claim 'Esse is percipi' leads to contradictions (as opposed to false, much to the chagrin of Kant?) - but if you want a decent brief summary to it all - just read the first few and last few pages.
I will re-read this once I have mastered everything about idealism and its variations (particularly Platonic idealism which is pretty damn cool!).