O. Henry, born William Sidney Porter in 1862, was a prolific American short story writer known for his narrative style and twist endings. After a troubled early life, which included a prison sentence for embezzlement, he emerged as O. Henry and published over 300 stories, with notable works like 'The Gift of the Magi' and 'The Ransom of Red Chief.' His writing was influenced by real-life experiences and emphasized the ordinary over the unexpected.