The real name of O. Henry is:

O’ Henry was the pseudonym of William Sydney Porter, an American short story writer.

O Henry: (1862-1910) pseudonym of William Sydney Porter. American short-story writer whose tales romanticized the commonplace—in particular the life of ordinary people in New York City.
O. Henry was a professional writer, he worked as a clerk in a drugstore.

Notable works: (Short stories )
- Heart of the West
- O. Henry Encore
- Roads of Destiny
- Sixes and Sevens
- Strictly Business
- The Four Million
- The Furnished Room
- The Gift of the Magi
- The Last Leaf
- The Ransom of Red Chief
- The Trimmed Lamp
- The Voice of the City
- Waifs and Strays
- Whirligigs

Source: Britannica.com