The Leslie speaker was designed by Don Leslie to work with the Hammond organ. However, Laurens Hammond, who invented the Hammond organ, hated Leslie and his designs and would not let any of his sales dealers sell the Leslie speakers.
It wasn’t until the jazz and then the rock ‘n’ roll players put the two together creating a completely different sound. And really, the Leslie speaker is just as an important part of the sound as the Hammond organ. It’s an amazing combination.