Klaus Baudelaire was the middle Baudelaire child and one of the main protagonists in A Series of Unfortunate Events.
Klaus is known to be the reader or researcher of his siblings. He remembers just about everything he reads, and this has helped the Baudelaire orphans immensely. He read a good deal of the Baudelaire library, and read what he could of the remains of the V.F.D. library, he also reads whatever he can read anywhere else.
Klaus is an avid reader. His favorite book is The Water Cycle, Volume 196, but he also enjoys books dealing with multiple wars. He remembers virtually everything he reads, retaining information which often helps the Baudelaires to escape from situations that their enemy, Count Olaf, leads them to and places them in. As a result of this appetite for books, he speaks many languages.
He is twelve years old at the beginning of the series, and turns thirteen in The Vile Village. By the end of the series, he is fourteen (fifteen years old if you count Chapter Fourteen). Klaus is the "bookworm" of the family, and his love of books has often helped him save himself and his sisters.
Hitler Parody Universe
Klaus has made several appearances throughout the Universe, such as when he gunned down Hitler, who was trying to ask regarding Fegelein's whereabouts, and when he was arrested. It was been established, however, that Klaus actually faked his death after the events of the series, and later lived under an assumed name as Heinrich Himmler.