Klaus Baudelaire

After the fire that kills their parents, Klaus and his sisters move in with Count Olaf. He's the first to distrust their guardian and keeps researching until he understands the plan: marry Violet in a play and grab the fortune.

When the scheme fails because Violet signs with her left hand, Klaus is the one who explains to Justice Strauss why the marriage doesn't count.

At Uncle Monty's house, Klaus devours the books on reptiles and helps his sisters unmask Stephano after their uncle's death. At Aunt Josephine's house, Klaus notices the grammar mistakes in the note she leaves behind and works out where she's hiding.

At the lumber mill, a fall breaks his glasses. The optometrist, Dr. Orwell, uses the appointment to hypnotize him, and Klaus starts following orders without realizing it, until the trance is broken.

At Prufrock, Klaus and his sisters befriend the Quagmire twins, whom Olaf kidnaps soon after. In the village of crows, the Baudelaires are accused of murder and jailed, and Klaus turns 13 inside the cell.

Before that, at the Squalors' penthouse, he's the one who notices an extra elevator door on the top floor, the clue that leads to their kidnapped friends. At Heimlich Hospital, he and Sunny dress as doctors to get Violet out of an operation set up by Olaf.

Separated from Sunny, Klaus climbs the Mortmain Mountains with Violet and finds Quigley Quagmire. On the submarine Queequeg, he dives into books looking for a cure for the fungus poisoning his little sister.

At the Hotel Denouement, the three work undercover as concierges to find out who J.S. is, the person who called the V.F.D. gathering. There and on the final island, Klaus is still the sibling who connects the clues about V.F.D. and their parents' past.

In the movie, Klaus is played by Liam Aiken. During the wedding play, he finds a big window fitted with lenses in Olaf's tower and realizes the villain used them to start the fire at the Baudelaire house. With the same lenses, he burns the marriage certificate and ruins the villain's whole scheme.

Louis Hynes plays Klaus in the Netflix series (2017–2019), his first professional role. In the 2004 movie, the role goes to Liam Aiken.