Horton the Elephant is a fictional character from the 1940 and 1954 Dr. Seuss books Horton Hatches the Egg, Horton Hears a Who!, and the television special and movie of the same name of the later book. He made his first flight in 2008 to celebrate the movie.  

Horton was not the only character from Dr. Seuss' books to be in the parade, though. The Cat in the Hat and the Grinch have made appearances, too. 

He first appeared in 2008 to promote the movie Horton Hears a Who! and retired after the 2010 parade.