“Doctor Evil”, if you please. I didn’t spend 6 years at Evil Medical School to be called “Mister”.
Thank you @gdave, like you and others said, wizards or scientists did it 
regarding the naming of superheroes.
Captain Marbles! You lost your marbles! (These are references to Mad Magazine #4: Superduperman!)
And if we add in medical “Doctor” titles:
“I’m Peter, by the way.”
“Doctor Strange.”
“Oh, we’re using our made-up names. Um…I’m Spider-Man then.”
Wait a tick… “the will to safeguard our shores”? So Captain America was supposed to be a captain for the Coast Guard? 
Gratitude alone should have risen him to Admiral America.
William Fawcett, founder of Fawcett Publishing, got his start after WW1 by basically self-publishing a humor magazine called Captain Billy’s Whiz Bang that was a huge success.
Right there, you have the source for CAPTAIN Marvel, BILLY Batson, and WHIZ Comics.
I don’t think it needed to be explained that a super-powered individual was a “marvel”. That said, a later story revealed that “MARVEL” is the acronym of the ancient Canaanite gods who gave the wizard Shazam his powers back in the day (though his magic word was actually “Vlarem”, I guess he anagrammed it into a real English word for the English-speaking Billy).
Interesting.
On a different, related comics question, was the name of Fawcett Publishing the inspiration of the name of the underground comics’ publisher “Kitchen Sink Press”? (faucet?)
I wonder if the reason relates to this question, where “captain” is a likely answer:
What is the highest ranking officer in the US military likely to be in front-line combat?
I’m sure that’s why “Captain” has been frequently used as a title for heroes in fiction, going back at least to the pulp days, because it’s the title used by the front line leader. Once you are promoted past that rank you’re probably drawing plans and relaying orders off the field.
Also I noticed TV Tropes has an entry on this phenomenon (because of course they do):
Captain Obvious isn’t a real captain either, or so he tells me.
In the animated series The Super Hero Squad Show, which was mostly aimed at kids, Captain America invites Wolverine to join the All-Captains Squad, provided that he change his name to Captain Canada. Other members of the Squad are Captain Britain, Captain Australia, Captain Brazil, and Captain Liechtenstein (“Like my country, I am small but financially stable!”).
what, no mention of the Myron Fass “Split” Captain Marvel? He was a magic robot built by aliens! Looking forward to the inevitable movie version.
https://misterkitty.org/extras/stupidcovers/stupidcomics247.html
Marvel Comics was launched in 1939. It became Marvel Mystery Comics with issue two. Mystery Men and Marvels were generic terms for comics heroes then. There was also a Dell character named Martan the Marvel Man and Centaur’s The Masked Marvel from 1939. Both preceded Captain Marvel by a year. The first Marvel Marvel was The Black Marvel from 1941, when the company was still named Timely.
You don’t have to dig too deep to understand Marvel as a name any more than you do Captain
I think that’s what the people need… A superhero who shows a little boy his ability to make his clothes invisible.
https://misterkitty.org/extras/stupidcovers/split2.jpg
Of CAPTAIN BILLY’S WHIZ BANG fame, famously referred to in The Music Man.
I concur heartily!
There were several brigadiers landed at D-Day.