What is known is that in 1943, Chicago produced a variation on pizzas. It has a coarse, crunchy crust, sauce on top of cheese and Italian sausage at its heart.
Italian sausage is the #1 pizza topping in the Chicago area (thankfully IMO), Pepperoni is #1 elsewhere in the US. I must be a true Chicago raised person as pepperoni is a pale second topping compared with sausage.
A toast to whoever invented deep dish, another slice please^