There are several different Alien races in the Marvel Comics' universe.

First appearances

• The A-Chiltarians in Tales to Astonish #46
• The Achernonians in Thor Annual #6
• The Alpha Centaurians in Sub-Mariner #7
• The Astrans in Hulk #6
• The Brood in Uncanny X-Men #155
• The Centurii in Thor #258
• The Deonists in Thor #261
• The Dire Wraiths in Rom the Spaceknight #1
• The Fomalhauti (as mutant race) in Thor #256, in Thor Annual #6
• The Froma in Tales of Suspense #68
• The Glx in Hulk #182
• The Gramosians in Thor #208
• The Grunds (as mutant race) in Thor #256, in Thor Annual Annual #6
• The Guna in Tales of Suspense #55
• The Horusians in Hulk #145
• The Judans in Strange Tales #180
• The Klklk in Hulk #273
• The Kosmosians in Tales to Astonish #44
• The Kree in Silver Surfer
• The Kronans in Journey into Mystery Vol. 1 #83
• The Kronans (as Stone Men from Saturn ) in Journey into Mystery #83
• The Kymellians in Power Pack #1
• The Lava Men (of Molto ) in Journey into Mystery #97, (of Jinku and his tribe) in Avengers #5, (of the tribe beneath ) Avengers #236
• The Malkuans in Strange Tales Vol. 1 #89
• The Rajaks in Tales of Suspense #57
• The Reptoids in Thor Annual #6
• The Rhunians in Thor #219
• The Rigellians (in assumed human form) in Thor #129, (in true form) in Thor #131
• The S'mggani in Hulk #230
• The Sagittarians in Hulk #111
• The Sarks in Strange Tales #179
• The Skrull in Fantastic Four ?
• The Shiar in X-men ?
• The Watchers (of Uatu) in Fantastic Four #13, in Tales of Suspense #53
• The Xarthans (as Carbon-Copy Men) in Journey into Mystery #90

References

• Official Handbook of the Marvel Universe: Deluxe Edition
  • #15: Wonder Man to Zzzax plus Alien races (March 1987)