Walt Disney found early success with a group of animated cartoons featuring a human (the "Alice" comedies); but he really hit pay dirt with his first animated star, Oswald the Lucky Rabbit.
Animator Ub Iwerks created Oswald in 1927 for a series of cartoons produced for distribution by Universal Studios. The quirky Oswald possessed many zany qualities. He embodied the craziness of the times and was a free spirited character unlike most other contemporary animated characters.
Disney Studios made only a few Oswald cartoons before Universal decided to take production in-house, thereby leaving Disney out of the process. (In response, Disney and Iwerks created a new character, a mouse, that would bring them their ultimate success.)
Oswald cartoons would continue to be produced into the 1940s; but, despite being Disney's first animated star, he had lost all rights to the character. Oswald was finally returned to the studio of his birth in 2006.
You can find the early Oswald cartoons here.