Answer by taking a quote from the following article:

Lyman Frank Baum (May 15, 1856 - May 6, 1919), better known as L. Frank Baum, was an American author chiefly famous for his children's books, particularly The Wonderful Wizard of Oz and its sequels. He wrote a total of 14 novels in the Oz series, plus 41 other novels, 83 short stories, over 200 poems, and at least 42 scripts. He made numerous attempts to bring his works to the stage and the nascent medium of film; the 1939 adaptation of the first Oz book would become a landmark of 20th century cinema. His works anticipated such century-later commonplaces as television, augmented reality, laptop computers (The Master Key), wireless telephones (Tik-Tok of Oz), women in high-risk and action-heavy occupations (Mary Louise in the Country), police corruption and false evidence (Phoebe Daring), and the ubiquity of advertising on clothing (Aunt Jane's Nieces at Work).

Baum embarked on his lifetime infatuation--and wavering financial success--with the theater. A local theatrical company duped him into replenishing their stock of costumes on the promise of leading roles coming his way. Disillusioned, Baum left the theater -- temporarily -- and went to work as a clerk in his brother-in-law's dry goods company in Syracuse. This experience may have influenced his story "The Suicide of Kiaros", first published in the literary journal The White Elephant. A fellow clerk one day was found locked in a store room dead, probably from suicide.  Baum could never stay away long from the stage. He performed in plays under the stage names of Louis F. Baum and George Brooks. In 1880, his father built him a theater in Richburg, New York, and Baum set about writing plays and gathering a company to act in them. The Maid of Arran proved a modest success, a melodrama with songs based on William Black's novel A Princess of Thule. Baum wrote the play and composed songs for it (making it a prototypical musical, as its songs relate to the narrative), and acted in the leading role. His aunt Katharine Gray played his character's aunt. She was the founder of Syracuse Oratory School, and Baum advertised his services in her catalog to teach theater, including stage business, play writing, directing, translating (French, German, and Italian), revision, and operettas.  On November 9, 1882, Baum married Maud Gage, a daughter of Matilda Joslyn Gage, a famous women's suffrage and feminist activist. While Baum was touring with The Maid of Arran, the theater in Richburg caught fire during a production of Baum's ironically titled parlor drama Matches, destroying the theater as well as the only known copies of many of Baum's scripts, including Matches, as well as costumes.

What is Baum's connection to the theater?
Baum embarked on his lifetime infatuation--and wavering financial success--with the theater.