When did medical certification start being a 'thing' in western cultures, ex. among US denizens, the British, etc.? In particular, who (organization, person, etc.) came up with the first standards when?
In speaking about preliminary medical certification, there are a few elements to consider: education, ethics codes, promotion of evidence based medicine and licensing.
Setting standards for education was the first undertaking, because through doing this it develops the idea of what is a "doctor" and what is not.
The first American medical school was the University of Pennsylvania, established 1765. The school was modeled on the University of Edinburgh.
Ethics Codes, Basic Standards
In the US, state and county level medical associations were developed in the 18th and 19th century to create these very elementary standards concerning the rights of patients, the duty of the doctor and to discuss the best ways to practice medicine. Doctors learned from each other what worked and what didn't, so that mistakes didn't need to be repeated.
The first state medical association was New Jersey, founded 1766.
From this grew a movement to create a national medical association and this became the American Medical Association, founded 1845.
Licensing In order to practice medicine in the US, you must have a license as well as a MD. To obtain this, doctors take examinations on a regular basis to prove their medical knowledge, known as the United States Medical Licensing Examination.
Licensing dates to as far back as the 1890s.