Question: Who created the fictional character that is the main protagonist and has an Uncle Henry in the Oz novels?

Context articles: Captain Salt in Oz
Peter Brown (Oz)
Uncle Henry (Oz)
Return to Oz
Joanna Dark
Dorothy Gale
Aunt Em
Charley Grapewin
Luke Skywalker
The Emerald City of Oz

Captain Salt in Oz (1936) is the thirtieth in the series of Oz novels created by L. Frank Baum and his successors, and the sixteenth written by Ruth Plumly Thompson.
 It was illustrated by John R. Neill.
Peter Brown is a major character in the Oz novels of Ruth Plumly Thompson, who continued the series of Oz books after the death of their creator, L. Frank Baum.
 Thompson used Peter as the protagonist in three of her books: "The Gnome King of Oz" (1927), "Jack Pumpkinhead of Oz" (1929), and "Pirates in Oz" (1931).
Uncle Henry is a fictional character from The Oz Books by L. Frank Baum.
 He is the uncle of orphan Dorothy Gale and husband of Aunt Em, and lived with them on a farm in Kansas.
Return to Oz is a 1985 fantasy adventure film directed and written by Walter Murch, an editor and sound designer, co-written by Gill Dennis and produced by Paul Maslansky.
 It stars Nicol Williamson as the Nome King, Jean Marsh as Princess Mombi, Piper Laurie as Aunt Em, Matt Clark as Uncle Henry and introduces Fairuza Balk as Dorothy Gale.
 It is loosely based on L. Frank Baum's "Oz" novels, mainly "The Marvelous Land of Oz" (1904) and "Ozma of Oz" (1907), yet is set six months after the events of the first novel, "The Wonderful Wizard of Oz" (1900) took place.
 Although it is not a sequel and unrelated to the 1939 Metro-Goldwyn-Mayer film, "The Wizard of Oz", it borrows a few elements of it such as the ruby slippers.
Joanna Dark is a fictional character and main protagonist of the "Perfect Dark" fictional universe, created by Rare.
 She made her debut in the Nintendo 64 first-person shooter "Perfect Dark" and is a player character in all the games of the series.
 Outside of video games, Joanna also appears as the lead character in all the "Perfect Dark" novels and comic books.
 Joanna is an operative for the fictional Carrington Institute, where she was given the code name "Perfect Dark" in honor of her flawless performance in training tests.
Dorothy Gale is a fictional character created by L. Frank Baum as the main protagonist in many of his "Oz" novels.
 She first appears in Baum's classic children's novel "The Wonderful Wizard of Oz" (1900) and reappears in most of its sequels.
 In addition, she is the main character in various adaptations, notably the classic 1939 film adaptation of the novel, "The Wizard of Oz".
Aunt Em is a fictional character from the Oz books.
 She is the aunt of Dorothy Gale and wife of Uncle Henry, and lives together with them on a farm in Kansas.
 In "The Wonderful Wizard of Oz", she is described as having been a "young, pretty wife" when she arrived at Uncle Henry's farm, but having been "grayed" by her life there, implying that she appears older than one might expect from her chronological age.
 Baum tells us that when Dorothy first came to live with her, Em would "scream and press her hand upon her heart" when startled by Dorothy's laughter, and she appears emotionally distant to her at the beginning of the story.
 However, after Dorothy is restored to her at the end of the book, we see her true nature: she cries out, "My darling child!"
 and covers her with kisses.
Charles Ellsworth Grapewin (December 20, 1869 – February 2, 1956), stage name Charley Grapewin, was an American vaudeville performer, writer and a stage and silent and sound actor, and comedian who was best known for portraying Aunt Em's husband, Uncle Henry in Metro-Goldwyn-Mayer's "The Wizard of Oz" (1939) as well as Grandpa Joad in "The Grapes of Wrath" (1940) and Jeeter Lester in "Tobacco Road" (1941).
 He usually portrayed elderly folksy-type characters in a rustic setting, in all appearing in over 100 films.
 He was the oldest cast member of The Wizard of Oz.
Luke Skywalker is a fictional character and the main protagonist of the original film trilogy of the "Star Wars" franchise created by George Lucas.
 The character, portrayed by Mark Hamill, is an important figure in the Rebel Alliance's struggle against the Galactic Empire.
 He is the twin brother of Rebellion leader Princess Leia Organa of Alderaan, a friend and brother-in-law of smuggler Han Solo, an apprentice to Jedi Masters Obi-Wan "Ben" Kenobi and Yoda, the son of fallen Jedi Anakin Skywalker (Darth Vader) and Queen of Naboo/Republic Senator Padmé Amidala and maternal uncle of Kylo Ren / Ben Solo.
 The now non-canon "Star Wars" expanded universe depicts him as a powerful Jedi Master, husband of Mara Jade, the father of Ben Skywalker and maternal uncle of Jaina, Jacen and Anakin Solo.
The Emerald City of Oz is the sixth of L. Frank Baum's fourteen Land of Oz books.
 It was also adapted into a Canadian animated film in 1987.
 Originally published on July 20, 1910, it is the story of Dorothy Gale and her Uncle Henry and Aunt Em coming to live in Oz permanently.
 While they are toured through the Quadling Country, the Nome King is assembling allies for an invasion of Oz.
 This is the first time in the Oz series that Baum made use of double plots for one of the books.