Final answer:
Paul Ehrlich developed Salvarsan against syphilis.
Step-by-step explanation:
The person who developed Salvarsan against syphilis, despite its arsenic-based toxicity, was Paul Ehrlich. In the early 1900s, Ehrlich set out to discover or synthesize chemical compounds capable of killing infectious microbes without harming the patient. One of Ehrlich's assistant, Sahachiro Hata, discovered Compound 606, which targeted the bacterium Treponema pallidum, the causative agent of syphilis, and was later marketed as Salvarsan.