Space races

In the setting of AD ASTRA, as in most space-opera comic book settings, the science fiction isn't meant to be rigorous, and to a purist, it isn't even science fiction at all.  Alien species in particular, are more notable assuming that they are interesting antagonists to fight rather than interesting alien societies to explore via fictional ethnography.

So, to explore this space a bit, I'm going to go through some of the major space-based Marvel alien races and what they are and why they're either important or interesting.  I'm using a very loose definition of "space" in this regard: the Negative Zone would count as well, since it provides a number of characters and races that are pretty much indistinguishable from aliens from regular space.  And for the heck of it, why not add the Microverse into the mix as well?

• The Badoon: a sexually segregated reptilian race that has often been seen as the butt of many jokes by other cosmic races.  Despite this, the Badoon control a large percentage of the Milky Way Galaxy, and are frequent antagonists for various superhero teams.  Major Victory, the original leader of the Guardians of the Galaxy team (which doesn't very closely resemble the more familiar Guardians of the Galaxy team in the movie) is a time-traveling character who warns us that the Badoon should be taken more seriously as they will end up being the major military threat in the galaxy in the future.
• The Brood: from X-Men comics, this race is basically wise-cracking Aliens; they look like aliens and they reproduce parasitically, like Aliens.  They fly around in space in giant starsharks; bio-engineered sharks that fly through space and have Aliens living in them (yes, you actually read that right.)  Like other Alien-inspired races (such as Warhammer 40k's Tyrannids) they have weird, gigantic heads, chitinous bodies, and are vaguely insectile.
• The Celestials: gigantic and inscrutible robots(?) from the stars that show up--sometimes--on planets and judge their inhabitants.  If they are found wanting, they are exterminated.  The run-up to Thor #400 (back in early 1988) was one of the first places that I really read much about them (although I was vaguely familiar with them from some earlier Eternals and What If? comics) and show clearly that they are pretty far beyond the ken of even the mightiest superheroes.  They have an interesting Erich von Daniken like vibe to them, especially in their role as medlers in the DNA of the Eternals and Deviants.
• The Dire Wraiths are an offshoot of the Skrulls, apparently, but that doesn't matter much because they are really kind of their own thing for the most part.  As the primary antagonists of Rom the Space-Knight (I actually had some of these back in the early to mid-80s) they'd have been pretty obscure, but they've also managed to make appearances in X-Men and the Avengers from time to time, and even Dr. Strange has tangled with them.  They are weird shape-shifting sorcerous aliens; in their natural form, red-clawed and beaked creatures with a long, barbed tongue.
• The Eternals are supposedly Celestial-made experiments with Earth DNA; basically, humans turned into gods, with superhero like powers and long-life.  While the Titanians and Uranians were originally unrelated, it was later decided--and they were retconned as such--that they were also Eternals.  The Eternals was an odd creation by Jack Kirby, who was experimenting (he did the same thing with New Gods by DC, which is basically the same idea) with van Daniken style science fiction with comic book superheroes and mythology.  As an aside, the Eternal character, identified much later as such, that has probably made the most rounds in the Marvel universe is Hyperion, who as originally created as a ersatz Superman.  This gives some idea of the level of power that the Eternals are meant to wield; if they were more mainstream, they'd be among the most powerful superheroes we'd see.
• The Inhumans actually have a very similar back-story to the Eternals, except the Kree rather than the Celestials are behind their genetic tampering.  This is the result of the Eternals originally having been meant to be independent rather than a canonical part of the Marvel Universe.  Now that they both are in it, they kind of overlap conceptually.  The Inhumans are often given the short end of various deals throughout their history.  Finally, when it's revealed that their king Black Bolt (Blackagar Boltagon is his real name.  I wish I were kidding about that, but I'm not) was replaced by a shape-shifting skrull spy, they decide that they've had enough, they take their entire civilization into space to the Kree homeworld, where they conquer the Kree Empire, and Black Bolt becomes the king of the Kree.  He later appears to be killed while fighting Emperor Vulcan, who is Emperor of the Shi'ar at the time, but since the only comic book character who reliably stays dead is Uncle Ben, of course he eventually comes back.  They also tussle with Thanos, which destroys their home city, but as a side effect of which, the Terrigenisis Bomb turns all kinds of sleeper half-inhumans on earth into either monsters or superheroes.  There's a movie coming out in 2019 about these guys, and the second season of Agents of S.H.I.E.L.D. debuts them officially in the Cinematic Universe.
• The Kree: originally debuted in the Fantastic Four (it's a real shame; these aren't really the most interesting characters in the Marvel universe, but they always seem to have the best villains).  Nominally blue-skinned, although regular human-looking Kree are also shown; the Kree are technologically advanced, super-strong and super-fast, making them basic shock-troops for superheroes to face, and with "name level" characters are leaders, captains, etc.  Some notable Kree characters include Captain Marvel, Marvel Boy, and Ronan the Accuser, the last well-known from the recent Guardians of the Galaxy movie, although of course he was already well-known in comics prior to that.  They are usually ruled by the Supreme Intelligence, a kind of post-humous conglomeration of the greatest minds of Kree society all turned into a hive-mind like entity.  A notable element of Kree appearances is their constant attempts to jump-start their evolution, which has supposedly been stagnant for millions of years, thanks to a curse by the Crystal of Ultimate Vision.  Hey, I told you that this isn't real science fiction, right?
• The Phalanx is another parasitic race; a hivemind of those infected with the transmode virus, which basically makes them into weird robotic/cybernetic creatures, who turn organic material into technology (whatever exactly that means) and then drain it of energy in order to feed.  In this, they are actually mimicking their "fathers" the Technarchs, who are--unlike the Phalanx--strictly and fiercely individualistic.  Phalanx can also shape-shift and quickly regenerate damage via absorbing techno-organic life force and then converting that into new techno-organic "tissue."
• The Shi'ar are one of the three superpowers of Marvel Intersteller, being a human-like race (with feathers instead of hair) with a war-like culture who have managed to put together a multi-ethnic empire of largely conquered peoples.  They feature prominently in X-Men stories, and have had a major impact on the Summers family in particular, since they kidnapped Ma and Pa Summers (Pa Summers became Corsair, the leader of the Starjammers until that role was taken by his son Alex Summers, also known as Havoc) and the Empire was even ruled briefly by Alex's younger brother Gabriel Summers, the "Omega level" mutant Vulcan.  Marvel editor Ed Brubacker specifically likened the Shi'ar to the Romulans; mean, war-like, and aggressive.  As an interesting aside, the champions and royal bodyguard of the Emperor D'Ken is the Imperial Guard, a bunch of non-Shi'ar citizens of the Empire who are transparently modeled on rival DC's Legion of Superheroes, including Gladiator, a kind of purple-skinned mohawk sporting Superman.
• The Skrulls are another Fantastic Four antagonist, which have since gone far beyond that in terms of scope.  A reptilian shape-shifter race, they were one of three superpowers in space--along with the Shi'ar and the Kree--for many years.  This has changed in recent years, their fleet and homeworld were destroyed by Galactus.  The balkanized remnants of the Empire were easy pickings for Shi'ar and Kree forces alike.  The Inhumans annihilate what's left of the Skrull Armada.  The Annihilation Wave destroys much of what is left of the Skrull inhabited planets.  Queen-Prophetess Veranke leads the Secret Invasion in a desperate attempt to reclaim Skrull power by taking over the Earth (not sure if that's really ever explained) which fails, putting the Skrulls even further behind.  While they're still guys who show up a fair bit in the comics, we're clearly meant to infer that their days as a intergalactic superpower are over.
• Xandar and the Nova Corps are a kind of answer to the Green Lantern Corps of DC, although their powers are much more modest.  Poor Xander, which is threatened with being blown up in the Guardians of the Galaxy movie was actually blown up no fewer than three times in the comic books.  Xandarians appear to be human physically, but since most of the ones we meet are members of the Nova Corps or are heralds of Galactus, empowered with the Power Cosmic, we never seem to meet one that isn't a powerful superhero of some sort or another.

Anyway, I could go through a similar exercise with DC or Wildstorm or any other imprint (although I admit to not being nearly as familiar with them as I am with Marvel) but from the above, you get the idea of what I'm looking for.  There isn't (in my experience) any reason to go beyond the Milky Way and maybe it's satellites within the Local Group, but when you do so, and you want basically aliens that are aggressive, sometimes monstrous, but often anthropomorphic to various degrees, including fully human appearing, and with high techno-babble equipment and often with superpowers that make them more than a match for regular folks, but peers with your average superheroes.

A collection of many of the space-themed characters of the Marvel Universe.  If you don't recognize Thanos and Galactus, at the very least, you simply can't call yourself a comic book fan, in my opinion.