A glance at the Peoples of Mongo list will reveal some obvious inconsistencies in how they are named. In 1934, the first year of the Flash Gordon comic strip, there are Lionmen and Hawkmen as well as Shark Men and Red Monkey Men. For the sake of consistency, should it not be Lion Men and Hawk Men to match the latter two or Sharkmen and Red Monkeymen to match the former pair? Alas, in 1935, we are introduced not to Tuskmen or Tusk Men, but to Tusk-Men. Hyphenated. Whether it's ___men, ___ Men, or ___-Men, it's an unfortunate masculine emphasis that ignores the ___women, ___ Women, and ___-Women. All of this is avoided by the Fire People who appear in November 1935 and the Sea Folk who appear in April 1936. Meanwhile, you have Prince Barin's followers who are known variously as Tree Men, Forest People, or Arborians. Arborians is the first instance of a people of Mongo who are named for a specific geographic location. They will be followed by the Frigians in 1939 and the Tropicans in 1940.
What a mess.
Obviously, Alex Raymond and Don Moore couldn't be bothered to concern themselves with consistency when it came to naming (or spelling) things, but I can. For the sake of running The Savage World of Flash Gordon or any other role-playing adaptation of Flash Gordon in a manner that doesn't make my editing muscles twitch, I am instituting the following:
All peoples of Mongo will be known as ___ People or by a name derived from their geographic origin. Individuals may be identified as ___ Man, ___ Woman, or ___ Person as appropriate.
This is not meant to be a lecture on gender identification or anything of the sort. This is just my own solution to sloppiness. Please feel free to adopt it in your own games and fan fiction.