The Music Man

In July 1912, a traveling salesman, "Professor" Harold Hill (Robert Preston), arrives in River City, Iowa, intrigued by the challenge of swindling the famously stubborn natives of Iowa ("Iowa Stubborn"). Masquerading as a traveling band instructor, Hill plans to con the citizens of River City into paying him to create a boys' marching band, including instruments, uniforms, and music instruction books. Once he has collected the money and the instruments and uniforms have arrived, he will hop the next train out of town, leaving them without their money or a band.
With help from his associate Marcellus Washburn (Buddy Hackett), Hill deliberately incites mass concern among the parents of River City that their young boys are being seduced into a world of sin and vice by the new pool table in town ("Ya Got Trouble"). He convinces them that a boys' marching band is the only way to keep the boys of the town out of trouble, and begins collecting their money ("76 Trombones"). Hill anticipates that Marian (Shirley Jones), the town's librarian and piano instructor, will attempt to discredit him, so he sets out to seduce her into silence. Also in opposition to Hill is the town's Mayor Shinn (Paul Ford), the owner of the billiard parlor where the new pool table has been installed, who orders the school board (portrayed by the barbershop quartet, The Buffalo Bills) to obtain Hill's credentials. When they attempt to do so, Hill avoids their questions by teaching them to sing as a barbershop quartet via "sustained talking." They are thereafter easily tricked by Hill into breaking into song whenever they ask for his credentials ("Sincere", "Pick-a-Little, Talk-a-Little/Goodnight Ladies", and "Lida Rose").
Meanwhile, Hill attempts to woo Marian, who has an extreme distrust of men. His charms have little effect upon Marian ("Marian the Librarian") despite his winning the admiration of her mother ("Gary, Indiana") and his attempts to draw out her unhappy younger brother Winthrop (Ronny Howard). When Marian discovers in the Indiana State Journal of Education 1890â1910 that Hill's claim to being "Gary Conservatory, Gold Medal, Class of '05" is a lie (Gary was founded in 1906), she attempts to present the evidence to Mayor Shinn and expose Hill as a fraud, but is momentarily interrupted by the arrival of the Wells Fargo wagon ("Wells Fargo Wagon"). When Winthrop, after years of moody withdrawal, joins in with the townspeople and speaks effusively with Marian due to the excitement at receiving his cornet, Marian begins to fall in love with Hill and subsequently hides the evidence she has uncovered from Mayor Shinn. Hill tells the boys to learn to play via the "Think System," in which they simply have to think of a tune over and over and will know how to play it without ever touching their instruments.
Meanwhile, Marian is falling more in love with Harold, and in a counterpart with The Buffalo Bills they sing "Lida Rose/Will I Ever Tell You". Hill's con is nearly complete; all he has to do is collect the rest of the instrument and uniform money, and he can disappear. During his meeting with Marian at the footbridge, the first time she has ever been there with a man, he learns that she knew of his deception but didn't tell because she is in love with him ("Till There Was You"). He is about to leave town when Charlie Cowell, a disgruntled anvil salesman who had been run out of Brighton, Illinois because Hill had conned the townspeople there, comes to River City and exposes Hill. Sought by an angry mob and pressed to leave town by Marcellus and Marian, Hill realizes that he is in love with Marian and can't leave River City ("Till There Was You (Reprise)"). He is captured by the mob and brought before a town meeting to be tarred and feathered. Marian defends Hill, and the townspeople, reminded of how he has brought so many of them together by his presence there, elect not to have him tarred and feathered. Mayor Shinn in response reminds the townspeople of how much money Hill has taken from them to form a band, with no apparent result. When he loudly demands to know "Where's the band?" Hill is saved by the town's boys, who have learned to play Beethoven's Minuet in G on their instruments. Although their technical expertise leaves much to be desired, the boys' parents are enthralled. As the boys in the band march out of the town hall, they are suddenly "transformed" into a spectacular marching band dressed in resplendent uniforms, and playing and marching with perfection, led by Hill. ("76 Trombones 2nd Reprise").

Question: Who is Marian?
Answer: The town's librarian and piano instructor.