Klaus (left) on the edge of Lake Lachrymose in the film.
Klaus Baudelaire is the middle Baudelaire child, and, though only thirteen years old, has read more books than most people do in a lifetime. He is always there to help Violet and Sunny with words they don't understand and has a photographic memory. He first appeared in The Bad Beginning, and appeared in each of the other twelve novels.
Biography
The Bad Beginning
Klaus lived with his parents until he was twelve years old, at which time his house was burned to the ground by Count Olaf while he and his siblings, Violet and Sunny, were playing at Briny Beach. The Baudelaire parents were killed in the fire, making Klaus and orphan. He and his siblings were sent to live with the evil Count Olaf, who forced them to do all of his chores and treated them abysmally. He tried to gain control of the fantastic Baudelaire fortune by tricking Violet into marrying him during a play, but due to Klaus's researching skills his plot was foiled, and Olaf was almost arrested, although he escaped due to the incompetence of Mr. Poe, the banker in charge of taking care of the Baudelaire orphans.
The Reptile Room
Klaus was transfered to uncle Monty, their new guardian. They live a kind of peaceful life, and they are ready to go to Peru when Stephano (Count Olaf) becomes uncle Monty's assistant. Stephano murders Uncle Monty but thanks to violet's invention of a lockpick and klaus's research about mambu du mal they make Mr. Poe realize that he is count olaf.
The Wide Window
Klaus and his sibling were transfered to Aunt Josephine. His only toy there was a rattle. Captain Sham(Count Olaf)appears and threatens Josephine to write a note that will leave the children to his care. Josephine faked her death.Klaus then decode a message fro Aunt Josephine's suicidal note. It read curdled cave. They went there and convinced Josephine to come back. Josephine didn't want to so Klaus said that the cave was for sale and there will be realtors. Klaus sees Aunt Josephine get thrown to the leeches and calls Olaf a fiend.
The Miserable Mill
He worked at Lucky Smells Lumbermill and got paid in coupons, which was later revealed to be illegal.
The Austere Academy
Klaus and his siblings met Duncan and Isadora Quagmire when they were sent to a boarding school; Prufrock Preparatory School. A friendship developed between Klaus and Isadora, from whom Klaus learned the usefulness of a case book.
The Ersatz Elevator
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The Vile Village
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The Hostile Hospital
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The Carnivorous Carnival
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The Slippery Slope
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The Grim Grotto
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The Penultimate Peril
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The End
Despite all of Lemony Snicket's research and hard work, he still does not know the current location, position and status of the Baudelaire children, so it is not known what happened to Klaus.
In The Reptile Room, it is said that Klaus would spend a lot of time thinking about his present situation many years later, so it is implied that he had survived. He and the siblings found themselves in the Star Trek and Battlestar Galactica universes.
Klaus and his siblings suffered a major loss when the Baudelaire fortune was ultimately destroyed in a battle between the Cardassians, Colonials, Cylons, Klingons, Romulans, and Starfleet. The Baudelaires manage to escape with the Great Unknown to the Battlestar Galactica universe.
He was once again sucked into the Great Unknown, this time onboard the Cylon basestar in the Battlestar Galactica universe. A Number Five maims Klaus by destroying his left eye, making him semi-blind. In retaliation, Klaus and Violet kill a Five, and the Baudelaires escaped the basestar, only to be taken again by the Great Unknown.
They found themselves standing in front of the Dalek Emperor in the Doctor Who universe. They dashed out, and as the Daleks open fire on them, they are quickly taken, this time in the same universe, but with the Cybermen. The Cybermen attempted to kill them, and the Baudelaires destroy these Cybermen as well. The orphans were then taken by the Great Unknown to their original universe.
Personal Attributes
Klaus has always had a love for books and the ability to retain all the information he encounters. This makes him an excellent researcher, and his researching skills often help the Baudelaire children to foil Count Olaf's evil schemes.
He wears glasses, and can barely see without them.