Two versions here. The 1st with Organ lead and 2nd, starting at 1:05 with Horn Lead.
Welcome to the greatest show on earth. This is by far the most famous piece of music associated with the circus, clowns and all around wacky fun.
Julius Fucik (Yep that was his real last name) was a Czech composer and conductor of military bands. His worldwide reputation rests primarily on “Entrance of the Gladiators” which is widely recognized, often under the title “Thunder and Blazes”, as one of the most popular theme tunes for circus clowns