| Name | Source | Type | |
|---|---|---|---|
| X-ists | |||
| X Parasites | Metroid Fusion | ||
| Xandarians | Humanoid | ||
| Xanthuans | |||
| Xarians | Battlelords of the 23rd Century | ||
| Xarquids | |||
| Xchagger | Star Control | ||
| Xeelee Sequence novels | an enigmatic and supremely powerful Kardashev Type V alien civilization | ||
| StarCraft | |||
| Star Trek | |||
| Alien movies | Parasitic | ||
| Xiangs | 2300 AD | ||
| Humanoid | |||
| Xilians | Invasion of Astro-Monster and | Humanoid | |
| Star Trek | Humanoid | ||
| Sonic the Hedgehog comics | |||
| Xxcha | Twilight Imperium | Peaceful arboreal testudinoids | |
| Star Trek |