Someone responsible for coming up with an idea so brilliant that it makes you wonder how no one else had ever thought of it before.
Wesley: These Mini-Reubens - with a little sauerkraut and a little swiss inside, - what mad genius brought these into the world? (Eats one) Mmm.
Something that 2 kids made up that means really genius and smart but more than that.
Girl A: You're mad genius Katie.
Girl B: No Syrus is.