Penicillin was discovered by Scottish scientist Alexander Fleming in 1928. He also did most of the early research that led to the mass production of it about a decade later.
Not so much as a scientist, although he holds more honorary doctorates (Oxford and Cambridge, among them) than he can count on two hands. His major contribution to science is popularizing it through his documentaries.
The contribution of Aristotle to biology is seen in various aspects. He made a major contribution in the theory of evolution but lacked the insight to complete it.