William Hickling Prescott (May 4, 1796 – January 28, 1859) was an American historian and Hispanist, who is widely recognized by historiographers to have been the first American scientific historian. Despite having serious visual impairment, which at times prevented him from reading or writing for himself, Prescott became one of the most eminent historians of 19th-century America. He is also noted for his eidetic memory, also called "photographic memory".

After an extensive period of study, during which he sporadically contributed to academic journals, Prescott specialized in late Renaissance Spain and the early Spanish Empire. His works on the subject, The History of the Reign of Ferdinand and Isabella the Catholic (1837), The History of the Conquest of Mexico (1843), A History of the Conquest of Peru (1847) and the unfinished History of the Reign of Phillip II (1856–1858) have become classic works in the field, and have had a great impact on the study of both Spain and Mesoamerica. During his lifetime, he was regarded as one of the greatest living American intellectuals and personally knew many of the leading political figures of the day, both in the United States and Britain. Prescott has become one of the most widely translated American historians and was an important figure in the development of history as a rigorous academic discipline.

Historians admire Prescott for his exhaustive, careful, and systematic use of archives, his accurate recreation of sequences of events, his balanced judgments, and his lively writing style. He was primarily focused on political and military affairs, largely ignoring the economic, social, intellectual, and cultural forces that historians have focused on in recent decades. Instead, he wrote narrative history, subsuming unstated causal forces in his driving storyline.

William H. Prescott was born in Salem, Massachusetts on May 4, 1796, the first of seven children, although four of his siblings died in infancy. His parents were William Prescott Jr., a lawyer, and his wife, née Catherine Greene Hickling. His grandfather William Prescott served as a colonel during the American Revolutionary War.

Prescott began formal schooling at the age of seven, studying under Mr. Jacob Knapp. The family moved to Boston, Massachusetts in 1808, where his father's earnings substantially increased. His studies continued under Dr. John Gardiner, rector of Trinity Episcopal Church. As a young man, Prescott frequented the Boston Athenæum, which at the time held the 10,000-volume private library of John Quincy Adams, who was on a diplomatic mission to Russia. In 1832, Prescott became a trustee of the library, a position he held for 15 years.

Prescott enrolled at Harvard College as a second year student (sophomore) in August 1811, at the age of 15. He was not considered academically distinguished, despite showing promise in Latin and Greek. Prescott found mathematics particularly difficult and resorted to memorizing mathematical demonstrations word-for-word, which he could do with relative ease, in order to hide his ignorance of the subject. Prescott's eyesight degenerated after being hit in the eye with a crust of bread during a food fight as a student, and it remained weak and unstable throughout the rest of his life. Prescott was admitted to Phi Beta Kappa society as a senior, which he considered a great personal honor, and graduated from Harvard in 1814. After a short period of rheumatic illness, he embarked on an extended tour of Europe.

Prescott first traveled to the Portuguese island of São Miguel in the Azores archipelago, where his grandfather and Portuguese grandmother lived. After two weeks, he left for the cooler climate of London, where he stayed with the distinguished surgeon Astley Cooper and the oculist William Adams. Prescott first used a noctograph while staying with Adams; the tool became a permanent feature of his life, allowing him to write independently in spite of his impaired eyesight. He visited Hampton Court Palace with future American president John Quincy Adams, at the time a diplomat in London, where they saw the Raphael Cartoons. In August 1816, Prescott traveled to Paris, but later moved on to Italy, where he spent the winter. He returned to Paris in early 1817, where he chanced to meet the American Hispanist George Ticknor, and made another visit to England. Prescott spent some time in Cambridge, where he saw the manuscripts of Isaac Newton's works, and returned to the United States in the same year. Prescott's first academic work, an essay submitted anonymously, was rejected by the North American Review in late 1817. After a short period of courtship, he married Susan Amory, the daughter of American poet Thomas Coffin Amory and Hannah Rowe Linzee, on May 4, 1820.

In 1821, Prescott abandoned the idea of a legal career because of the continued deterioration of his eyesight and resolved to devote himself to literature. Although he initially studied a wide range of subjects, including Italian, French, English and Spanish literature, American history, classics and political philosophy, Prescott came to focus on Italian poetry. Among the works he studied during this period were such classics as Dante's Divine Comedy and Boccaccio's Decameron. His first published works were two essays in the North American Review—both discussing Italian poetry. The first of these, published in 1824, was titled Italian Narrative Poetry, and became somewhat controversial after it was heavily criticized in an Italian review by Lorenzo Da Ponte, the librettist of Mozart's Don Giovanni. Prescott wrote a succinct reply to Da Ponte's fifty-page argument in the North American Review of July 1825. Da Ponte published the criticisms as an appendix to his translation of Dodley's Economy of Human life, which resulted in Prescott noticing them rather late.