Klaus Baudelaire is one of the main characters in the children's book

Children's literature

Children's literature is for readers and listeners up to about age twelve; it is often defined in four different ways: books written by children, books written for children, books chosen by children, or books chosen for children. It is often illustrated. The term is used in senses which sometimes...

 series, A Series of Unfortunate Events

A Series of Unfortunate Events

A Series of Unfortunate Events is a series of children's novels by Lemony Snicket which follows the turbulent lives of Violet, Klaus, and Sunny Baudelaire after their parents' death in an arsonous house fire...

by Lemony Snicket

Lemony Snicket

Lemony Snicket is the pen name of American novelist Daniel Handler . Snicket is the author of several children's books, serving as the narrator of A Series of Unfortunate Events and appearing as a character within the series. Because of this, the name Lemony Snicket may refer to both a fictional...

 who appears in all thirteen novels. Klaus is the middle child of the Baudelaire orphan

Orphan

An orphan is a child permanently bereaved of or abandoned by his or her parents. In common usage, only a child who has lost both parents is called an orphan...

s; he has an older sister named Violet

Violet Baudelaire

Violet Baudelaire is one of the main characters in the children's book series A Series of Unfortunate Events by Lemony Snicket and appears in all thirteen books. She is the oldest of the Baudelaire orphans at 14 years old, and often helps her 12-year-old brother Klaus and her baby sister Sunny...

 and a younger sister named Sunny

Sunny Baudelaire

Sunny Baudelaire is one of the protagonists of Lemony Snicket's novel series A Series of Unfortunate Events. Sunny is the youngest of the three Baudelaire orphans, and is described as an infant through much of the series...

. His sister Violet is the family inventor, Sunny is the family biter (and later chef) and Klaus is the researcher. He is twelve years old at the beginning of the series, and turns thirteen in The Vile Village

The Vile Village

The Vile Village is the seventh novel in the book series A Series of Unfortunate Events by Lemony Snicket. After escaping Olaf once again, the Baudelaire orphans are taken into the care of a whole village, only to find lots of rules and chores, evil seniors, and Count Olaf and his evil girlfriend...

.