The Outlaws of Sherwood is a retelling of the legend of Robin Hood by Robin McKinley.
 In McKinley's afterword, she says, "The retellings through the centuries have echoed concurrent preoccupations."
 The story includes both the traditional Robin Hood characters — Little John, Much, Friar Tuck, Marian and Alan-a-dale — and characters of McKinley's own invention.
 Notably, three of the most important characters are women, all of whom escape marriage to prospective spouses chosen by their fathers.
Deerskin is a dark fantasy novel by Robin McKinley, first published in 1993.
 It is based on an old French fairy tale by Charles Perrault called "Peau d'âne" (English translation: "Donkeyskin").
 It was nominated for the Mythopoeic Fantasy Award for Adult Literature.
A Knot in the Grain and other Stories is a collection of short fantasy stories by author and Newbery Medalist, Robin McKinley.
 Published by HarperTrophy, this collection of stories came out in 1994 although several of the stories had been previously printed.
 This collection gives readers a taste of McKinley's style and allows brief glimpses in the worlds where magic lives and you never know what might be possible.
Chalice is a novel by American fantasy author Robin McKinley.
 It was published in 2008 (New York: G. P. Putnam's Sons).
Jennifer Carolyn Robin McKinley (born November 16, 1952), known as Robin McKinley, is an American author of fantasy and children's books.
 Her 1984 novel "The Hero and the Crown" won the Newbery Medal as the year's best new American children's book.
The Blue Sword is a fantasy novel written by American author Robin McKinley and published by Greenwillow Books in 1982.
 The novel "The Hero and the Crown" serves as a prequel.
 "The Blue Sword" has received several awards, including: Newbery Honor Award, ALA Best Book for Young Adults and the ALA Notable Children's Book.
 The story, told in the third-person omniscient perspective, is of a young woman named Angharad Crewe, called Harry, who becomes a warrior in her adopted homeland of Damar.
Rose Daughter is a retelling of the fairytale "Beauty and the Beast" by Robin McKinley, published in 1997.
 It is the second retelling of the tale that McKinley has written: the first being her 1978 story, Beauty: A Retelling of the Story of Beauty & the Beast.
William Sydney Porter (September 11, 1862 – June 5, 1910), known by his pen name O. Henry, was an American short story writer.
 His stories are known for their surprise endings.
The Hero and the Crown is a fantasy novel written by Robin McKinley and published by Greenwillow Books in 1984.
 It is the winner of the 1985 Newbery Medal award.
 The book is the prequel to "The Blue Sword", written in 1982.
 This story focuses on "Aerin Dragon-Killer," also known as "Aerin Firehair," the heroine who is introduced as a legendary character in "The Blue Sword".
 The book narrates Aerin's evolution from the shy, retiring daughter of the King of Damar to the heroic queen who protects her people from the demonic Northerners.
The Door in the Hedge is a collection of fairy tales by Robin McKinley, published by William Morrow and Company under its Greenwillow Books imprint in 1981.
 It includes two original stories and two retellings.

Question: Who wrote children's books O. Henry or Robin McKinley?
Answer: Robin McKinley