Origin of idiom "wearing the < role > hat?"

Question

What is the origin of the idiom "wearing the < role > hat"?

Here is an example from the post Getting things done when you wear multiple hats in PookieMD's Blog:

I wear many hats, and I suppose you do as well. I wear my small business owner hat when I run/manage my company, ExtraMD, my doctor hat when I play doctor, and my consultant hat when I head off to multiple meetings that seem to define the EHR consultant world I live in. Of course, I wear my mother hat, wife hat, Girl Scout leader hat, and the hat that seems to get worn the least–the self hat.

and another example from Jean Scheid's The Many Hats of a Project Manager:

As the owner of a small auto dealership, many of my managers wear more than one hat. My service director is also my parts director and my finance manager is also my sales manager. In the business office, my controller has an added responsibility of obtaining registrations for the vehicles we sell.

Answer 1

There's a related discussion over at The Phrase Finder:

I think it comes from a time (not long ago) when everyone wore hats, and many of those hats were specific to a given trade, official position or function. So someone who had several roles would have several hats and would wear the appropriate one for the occasion. [...] "which hat will you be wearing?" would mean "in which capacity will you be attending?"

As you can see, it's just speculation without citing any sources, so I have looked it up in the American Heritage Dictionary of Idioms, and here's what it has to say:

wear another hat Also, wear a different hat or two hats; wear more than one hat. Function in a different or more than one capacity or position, as in I'm wearing another hat today; yesterday I was a housewife, today I'm an attorney, or I wear two hats—are you asking me as a member of the city council or as a storeowner? This metaphoric expression alludes to headgear worn for different occupations. [Mid-1900s]

So it's indeed a metaphor, and a relatively young one.

Answer 2

It may or may not be the original source of this usage of the term, but in a 1965 article on administration, Scientology founder L. Ron Hubbard wrote:

HAT: Slang for the title and work of a post in an org. Taken from the fact that in many professions such as railroading the type of hat worn is the badge for the job.

The article is a policy letter (article on the administration methods to be applied by Scientology Churches) from 1 July 1965—the third such issue on that particular day. Its title is "Hats, The Reason For."

The word "hat" with this meaning is used liberally throughout Scientology materials on administration, many of which date from the early 1960s.

There is an earlier article (policy letter) from 28 February 1957, titled simply "Hats," which seems to be one of the earliest usages of this particular definition by Mr. Hubbard.

It would not surprise me at all if that were the original source of this definition, though I have no evidence either way on that. (Proving a negative is difficult, but this at least aligns with the approximate dates mentioned in other answers.)

Answer 3

It's from an old Broadway couple who wrote and directed acted and produced between them.

They lived in a tiny apartment and found themselves getting in each other's way and startig conflict hwhere it needn't be.

They needed a code to communicate to the another when they were trying to focus on without having to break focus to look up and explain themselves so they chose their various hats because they lived in a time earlier int he 20th century when hats were more in fashion as part of a daily ensemble and not just for special occasions. When I wear my blue hat, I'm writing, when I wear my green hat I'm just lounging, etc.