Who was Max Planck, and how did he contribute to atomic theory? ( I need to explain this to a 6th grader)?

I have to do a newsletter on the development of the Atomic Theory and I need to do an article on Max Planck. I've researched him, but I don't really understand any of the research I've done - He's the father of Quantum mechanics, and that's one of the most complex fields on earth? I need to explain to a 6th grader what Max Planck did, and what his contribution to atomic theory was.