Who is Dr. John Snow in the book, The Ghost Map?

Dr. John Snow was a physician an anesthesiologist who had done pioneer work on the application of ether and chloroform to dull the pain of surgical procedures. Prior to his work, surgery patients had to grin and bear it. Queen Victoria was one of the first patients to use chloroform. She summoned Snow to administer the anesthesia during the birth of her eighth child. Snow was also interested in cholera epidemics and had done extensive research on an early outbreak in London.