Drug discovery is a result of humans seeking a solution for life threatening diseases that existed in the 19th century. Drug Discovery started as an offset of chemistry and has now become an interdisciplinary science.
Paul Ehrlich is regarded as the father of Chemotherapy. He was the first to identify that some dye's selectively stained bacteria but not human cells, and visualized the concept of treatment for bacterial diseases by chemical agents. He coined the term "Magic bullet" for these specific chemical agents. Ehrlich extensively worked on the dye, Methylene Blue, but it did not succeed clinically. However, his quest continued and he studied a number of arsenic containing compounds.
This resulted in the discovery of Compound '606' or Salvarsan which was used for the treatment of Syphilis. This was used in the treatment of Syphilis till the early 20th century after which Penicillin replaced Salvarsan.
He received the Nobel Prize in Physiology or Medicine in 1908.