William Sydney Porter (September 11, 1862 - June 5, 1910), known by his pen name O. Henry, was an American short story writer.

O. Henry's short stories are known for their wit, wordplay, warm characterization, and surprise endings.

William Sidney Porter was born on September 11, 1862, in Greensboro, North Carolina. He changed the spelling of his middle name to Sydney in 1898. His parents were Dr. Algernon Sidney Porter (1825-88), a physician, and Mary Jane Virginia Swaim Porter (1833-65). William's parents had married on April 20, 1858.

When William was three, his mother died from tuberculosis, and he and his father moved into the home of his paternal grandmother. As a child, Porter was always reading, everything from classics to dime novels; his favorite works were Lane's translation of One Thousand and One Nights, and Burton's Anatomy of Melancholy.