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 surprise endings.

Most of O. Henry's stories are set in his own time, the early 20th century. Many take place in New York City and deal for the most part with ordinary people: clerks, policemen, waitresses, etc.

O. Henry's work is wide-ranging, and his characters can be found roaming the cattle-lands of Texas, exploring the art of the con-man, or investigating the tensions of class and wealth in turn-of-the-century New York. O. Henry had an inimitable hand for isolating some element of society and describing it with an incredible economy and grace of language. Some of his best and least-known work is contained in Cabbages and Kings, a series of stories each of which explores some individual aspect of life in a paralytically sleepy Central American town, while advancing some aspect of the larger plot and relating back one to another.

Porter was a heavy drinker, and by 1908 his markedly deteriorating health affected his writing. In 1909, his second wife, Sarah, left him, and he died on June 5, 1910, of cirrhosis of the liver, complications of diabetes, and an enlarged heart. After funeral services in New York City, he was buried in the Riverside Cemetery in Asheville, North Carolina.