A pair of hardbitten alien soldiers enamored of Earth

Hawkman - Captain Mar-Vell

Quite fond of this one here— I always liked the way both of these characters looked…

I refer here to the Hawkman rejigged by Gardner Fox and Joe Kubert in 1961: a police officer from the planet Thanagar operating on Earth. Like the Silver Age re-introductions of the Flash, Green Lantern and the Atom, the Katar Hol iteration was introduced to the DC diaspora with a science fiction bent (as opposed to the Golden Age version, who has his own equivalent —to be named later).

Post-Crisis, Hawkman possibly suffered the most convolutions of any significant DC character. Pre-Crisis, Thanagar was said to have been one of many peaceful, technocratic societies so beloved of Silver Age DC, but it turned warlike in the late ‘70s, prompting Katar to turn against his race. In 1989, a mini-series called Hawkworld posited that Thanagar had been run by militaristic society for centuries, but the PTB at DC decided that this would take place in the present, thereby making Hol’s first “canonical” appearance contemporaneous and thus mooting all prior continuity. The Hawkman that had served in the JLA was now the Golden Age iteration.

Seems easy enough to say that, after Superboy’s multiverse-shuffling tantrum, that Katar Hol came to Earth from Thanagar, saw the error of his race’s ways, got the “Hawkman” mantle handed over to him by Carter Hall, and away we go: no harm no foul. Instead, the Hawkman franchise is incredibly convoluted. So you’ll forgive me if I go with my eminently sensible solution.

As for Mar-Vell…perhaps understandably, in 1967 Stan Lee wanted to lay claim to the copyright “Captain Marvel,” one that hadn’t been used by DC for the Big Red Cheese since the company won ownership of the character from its lawsuit against Fawcett (don’t ask about the short-lived 1966 version published by MF Enterprises). So Marvel’s version was a dissident Kree soldier on Earth.

No one seemed to know what to do with him at first: Roy Thomas rendered him akin to the "Big Red Cheese" by having him trade places with perennial hanger-on Rick Jones (one would languish in a nether-dimension while the other was on Earth). Finally, Jim Starlin made him a “Cosmic Protector,” with accompanying “cosmic awareness”—this is the version beloved by fandom. In 1982, Starlin had Mar-Vell die of cancer…25 years later, he’s plucked out of the timestream, just before cancer advances so that he can assist in the “Civil War” to no meaningful effect. He also was ret-conned into fathering Genis Vell and Kree/Skrull hybrid the Hulking—ahh, editorial mandates!

Note that the "Big Red Cheese" is the essentially the same person as Billy Batson and is otherwise not an extraterrestrial, so any match-up with Mar-Vell doesn’t work.

Commonalities:
Both are soldiers hailing from militaristic societies who come to Earth, renounce their race’s domineering ways, and champion their adopted world. Both take terran secret identities— HM: Carter Hall, CM: Walter Lawson.

Differences:
Well, Hol has them wings, is fond of archaic weaponry and otherwise boasts enhanced strength common to Thanagarians. He also had a partner/wife Shayera. Whereas Vell’s abilities shifted over time: he began as a Kree soldier and gained the powers mentioned above. His fellow Kree soldier, Una, never had a superhero guise, but as you will see below, I’m going to cheat.

Alternate histories:

CM: Mar Vell, a soldier from the expansionist interstellar society the Kree is stationed on Earth with his wife/colleague Una. The two renounce their homeworld and battle evil doers as Captain Marvel and Ms. Marvel (see who Carol Danvers is paired with at a later date) and join the Avengers.

HM: Katar Hol, a soldier from the expansionist interstellar society from Thanagar is stationed on Earth with his colleague/lover Shayera. The two renounce their homeworld, although Shayera is killed by another Thanagarian captain, leaving Hol to battle evil doers as Hawkman on Earth and in the cosmos (he finds time to co-exist with Snapper Carr and father some children as well). He often works with the Justice League, but eventually succumbs to cancer—that is, until an editorial mandate concocts a cheap ploy to resurrect him.