Alexander Fleming

Alexander Fleming was a human biologist in the early 20th century who discovered penicillin.

In an alternative timeline, Eric Charles Vincent murdered Fleming in a botched robbery in December 1927, some months before he would have discovered penicillin. Without the antibiotic, Earth fell prey to meningitis and pneumonia in 1956. Since the survivors never developed space travel, the Knights of Velyshaa were never defeated as they otherwise would have been. (BFA: The Sirens of Time)