Who is the brains behind making Lego structures work, and how is it designed

Not sure if this has been asked before, but who designs Lego sets? Do specified engineers design them? Is their some sort of mulit level course that needs to be accomplished? There's gotta be some sort of qualifications because the sets can be quite complex. My guess is an engineer degree and skills in 3d rendering and design or something, they have it in a computer, and whoever designs the sets can alter the variations. Anyone know?