List of fictional alien species: X
| Name | Source | Type |
|---|---|---|
| X-ists | Church of the SubGenius | |
| X-Nauts | Paper Mario: The Thousand-Year Door | |
| X Parasites | Metroid Fusion | |
| Xandarians | Marvel Comics | Humanoid |
| Xanthuans | DC Comics' Legion of Super-Heroes | |
| Battlelords of the 23rd Century | ||
| Xarquids | X-COM: Terror from the Deep | |
| Xchagger | Star Control | |
| Xel'Naga | StarCraft | |
| Star Trek | ||
| Xenomorphs | Alien movies | Parasitic |
| Xenu | Scientology | |
| 2300 AD | ||
| Xilians | Invasion of Astro-Monster and Godzilla: Final Wars | Humanoid |
| Xindi | Star Trek | Humanoid |
| Sonic the Hedgehog comics | ||
| Xxcha | Twilight Imperium | Peaceful arboreal testudinoids |
| Star Trek |
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- Lists of fictional alien species