Why are bosses called 'bosses'?

There were bosses in games ever since 1975, and I don't think I really have to define 'boss' here. But how did the word get stuck? And when was the first time when the challenging enemy was referred to as a 'boss'?

Sorry for the necro. I find this immensely interesting, and have done some deep digging and made a video about the topic:

The earliest source I found is from a 1980 arcade operating manual of Space Panic, mentioning bosses. Another enemy in that game is a 'don'.

In early 1980's Japan, "bosu" (loanword from English) had a derogatory connotation to do with Mafia. Translating "bosu" would give you "boss", but in English the negative meaning is not present.

Old Kung Fu films use this term for mobsters too (Bruce Lee in The Big Boss).

~ GeoKoer

From what I can find, the term's origin has been lost, however I did find some interesting details.

• The earliest usage seems to be from around 1983 in Joystick magazine, as discussed on Wikipedia.

Take a wild shot in Galaga-- you might fire (at) the Boss

• The term "Mini-Boss" appeared in the "Metroid" Instruction Booklet (referring to Kraid and Ridley, on page 15) when the game was released in 1986. Note that "Mother Brain" is not referred to as a "Boss" where she's discussed in the manual.
• "Boss" was spread more broadly by Nintendo Power, starting around 1988. I have a feeling that the term was coined inside of Nintendo as the magazine writers needed a term for the end-level baddies.
• The (translated) term "Boss" is also used in Japan. It might be that the term originated in Japan, but I have not found any information to back this up.