What book did O Henry write?

O. Henry, the pen name of William Sydney Porter, wrote many books, but his most famous work is a collection of short stories titled "The Gift of the Magi".

Some other popular books by O. Henry include:

* "The Four Million"

* "Cabbages and Kings"

* "The Roads of Destiny"

* "Heart of the West"

* "Whirligigs"

He was known for his clever twist endings and his stories often dealt with the lives of ordinary people in New York City.