In “Horton Hears a Who!”, the leader of Whoville holds the title of Mayor.
The Mayor is Horton’s main contact inside the microscopic city. In Dr. Seuss’s 1954 book, the character is identified by the civic title “Mayor,” without the expanded personal identity used in some later adaptations. The Mayor speaks for Whoville and helps explain that an entire population lives on the tiny speck Horton has discovered.
The 2008 animated film gives the character the name Mayor Ned McDodd. In that version, he is portrayed as part of a long line of Whoville mayors and as the father of 96 daughters and one son, JoJo. Those details belong specifically to the film and should not be treated as the wording of the original book.
A common mix-up is choosing “king” or “president,” since Whoville has a formal civic leader. The canonical title used in the story is Mayor.