Inventor: Alexander Fleming
What Happened: Halfway through an experiment with bacteria, Alexander Fleming up and went on vacation. Slob that he was, he left a dirty petri dish in the lab sink.
Big Discovery: When he got back, he found bacteria had grown all over the plate, except in an area where mold had formed.
As a Result: That discovery led to two things: 1) penicillin and 2) Mrs. Fleming hiring a maid.