Louis Pasteur was a historical figure. He was a renowned scientist.
In 2266, Dr. Roger Korby was described by Spock as the "Louis Pasteur of archaeological medicine." Korby's translations of the medical records from the Orion ruins revolutionized immunization techniques. (TOS: "What Are Little Girls Made Of?")
In 2371, Pasteur's name was among the choices The Doctor considered in giving himself, as stated in a discussion with Kes. This name was among other medical revolutionaries such as Pyong Ko, Jarvik and Schweitzer. (VOY: "Fury")