Sei Shōnagon, born in the year circa 967, was a Japanese author, poet, and court lady who served Empress Teishi (Sadako) during the middle Heian period. Known primarily for her literary work, The Pillow Book (makura no sōshi), Sei Shōnagon's contributions to Japanese literature have been celebrated for centuries. Her work is a meticulous diary that was traditionally kept under the pillow, hence its name. The Pillow Book is renowned for its unique format, comprising a series of lists that capture the daily realities, emotions, and observations of Heian period court life. These lists range from things that excite, to those that evoke a sense of uncleanliness, to incomparable experiences, showcasing her keen eye for the intricacies of her surroundings.

Her life, much like her real name, remains a subject of debate among historians. The most widely accepted theory proposes her name was Kiyohara Nagiko, derived from a combination of a bureaucratic title, "Shōnagon" (meaning third subsecretary of State), and her family name, "Sei" (the Chinese pronunciation of the first part of her surname, Kiyohara, which means "pure field"). Daughter of the poet Kiyohara no Motosuke, Sei Shōnagon leveraged her family's prominent position to become a lady-in-waiting to Empress Consort Fujiwara no Sadako, the favored wife of Emperor Ichijō.

Aside from The Pillow Book, she also authored a collection of poems known as Sei Shonagon-shu and is featured as one of the poets in the Ogura Hyakunin Isshu, a traditional Japanese card game that tests participants' memory and poetic knowledge. Sei Shōnagon's legacy as a writer and poet continues to be celebrated, with her work being selected, annotated, and translated by notable figures such as Jorge Luis Borges, with the help of María Kodama.