Opal Whiteley was an American nature writer and diarist who gained international fame for the publication of her childhood diary, which featured meditations and observations of nature and wildlife. Raised in logging camps in rural Oregon, Whiteley was considered by some a child prodigy, expressing intense interest in both writing and science in her youth.

As an adolescent, she began tutoring and holding lectures on natural history and geology in her community, earning a reputation as an amateur naturalist. She became a noted speaker for the Young People's Society of Christian Endeavour. While attending the University of Oregon, Whiteley toured the state giving lectures on nature and the environment.

In 1918, she self-published The Fairyland Around Us, which combined factual scientific information with mystical observations of nature. In 1919, she traveled to Boston to seek wider distribution of the book. There, she met Atlantic Monthly publisher Ellery Sedgwick, who instead suggested she publish her childhood diary. Over several months, Whiteley meticulously reassembled the diary, which was first released in serial form in the Atlantic Monthly in March 1920. It was later published in book format in September 1920 under the title The Story of Opal: The Journal of an Understanding Heart. The publication of the diary earned Whiteley international fame, though it was widely speculated she had written the work as an adult.

Throughout her life, Whiteley claimed to have been the biological daughter of the French naturalist Henri, Prince of Orléans, who died during an expedition in India in 1901. She frequently went by the name Françoise Marie de Bourbon-Orléans, in reference to her alleged father. The details surrounding her family history have been subject to wide speculation, with several biographers attributing the claims to delusions stemming from mental illness.

Following the publication of her diary, Whiteley relocated to England, where she was eventually committed to a psychiatric hospital in 1948. She spent the remainder of her life in psychiatric care until her death in 1992 at Napsbury Hospital.

In 1986, writer Benjamin Hoff published The Singing Creek where the Willows Grow: The Rediscovered Diary of Opal Whiteley, a biography accompanying her full diary, which won the National Book Award in 1988. The diary has been republished in several other editions, and Whiteley's life story has been adapted in film and theater productions.