Max Fleischer was a pioneer in the animation business, responsible for creating the animation technique of rotoscoping. This involved drawing animation on top of frames from a live action film. This animation technique went on to become an important part of Ralph Bakshi's animation style.
Fleischer was also responsible for introducing the first cartoons with sound in 1924. He used rotoscoping and sound to include popular contemporary jazz musicians of the time such as Cab Calloway and Louis Armstrong in his cartoons. In the Betty Boop cartoon "Minnie The Moocher" Cab Calloway is shown animated as a bizarre walrus like character performing all the insane body movements Cab is known for. He's also shown animated as a giant mutated horny freak with a white beard in "Old Man Of The Mountain".
To find a wide selection of Betty Boop cartoons that you can download, be sure to check out those available at archive.org.
Betty Boop - Minne The Moocher (With Cab Calloway)
Betty Boop - Old Man Of The Mountain (With Cab Calloway)