- Incubator
- Incursean
- Indogene
- Infestor
- Infi-Knight
- Ing
- Ingavi
- Ingclaw
- Inglet
- Inglet (Faster Than Light)
- Ingsmasher
- Ingsphere Cache
- Ingstorm
- Ingworm
- Ingworm Cache
- Inheritor
- Inhuman
- Inky
- Inleshat
- Inner Voice
- Inner Worlder
- Inquisitor Kryptman
- Insect-mandibles Alien
- Insect Aliens (The Twilight Zone)
- Insectioids of C'dante
- Insectoid
- Insectoid (Ben 10)
- Insectoid (Brewster Rockit)
- Insectoid (Gohan's Rage)
- Insectoid (Transformers: Cyberverse)
- Insectoid (Wildstorm)
- Insectoid Parasite
- Insectophagus
- Insectrox
- Inspector 13's Species
- Instant Martian
- Intarian
- Integral (Doctor Who)
- Integrated Data Entity
- Integrated Data Sentient Entity
- Intelligent Machine Alien
- Intelliton
- Inter-Species Reproduction
- Inter Minorian
- Interdimensional Being
- Interdimensional Bug
- Intergalactic Confederation
- Intergalactic Council of Superior Beings
- Intergalactic Vac Pac
- Interphasic Organism
- Interplanetary Alliance
- Interstellar Plankton
- Intersystem Union
- Inusannon
- Inuwashi Gunjin
- Inverse
- Invertroid
- Invid
- Invincible's Species
- Iog'g'gutth
- Ion Eel
- Iotian
- Iotran
- Ipharian-Da'Lor
- Iphigini
- Iraquinik Confederation
- Irathient
- Irax
- Irhennian
- Irian
- Iridescent Flint Beetle
- Irkburgle
- Irken
- Irnakk
- Iron Golem
- Ironak
- Ironclad Whale
- Irrasian
- Irrukiine
- Ish
- Isha
- Ishi Tib
- Isis (Star Trek)
- Iskalloni
- Iskani
- Iskoort
- Isle of the Deep
- Isolus
- Issori
- Istician
- It
- Italbosi
- Ithenite
- Ithorian
- Ithullan
- Itibian
- Ium
- Ivrooy Coral
- Iwadama
- Iwagen
- Ix'Idar
- Ixbee's species
- Ixion
- Ixll
- Ixplix
- Ixtl
- Iyaaran
- Iyra
- Izverg
- J'Onn's Species
- J'naii
- J-23 native
- J-Rod
- Jababian
- Jablee
- Jaboodie
- Jabori
- Jack-O-Lantern
- Jack-lizard
- Jack Jeebs' species
- Jack Ketch Tree
- Jackal Mastiff
- Jackworm
- Jade Chime Singer
- Jaffa
- Jaffee
- Jaftee
- Jagaroth
- JahSepp
- Jaig'alaar
- Jaime Reyes
- Jain Technology
- Jair
- Jakabird
- Jakelian
- Jakench
- Jakoosk
- Jalavash Worm
- Jallian
- Jam Pony
- Jandoonian
- Janice (Robotech)
- Janisi
- Janissary
- Janosian
- Jante (Species)
- Jarada
- Jardaan
- Jarell
- Jarencat
- Jargonian
- Jaridian
- Jarra's species
- Jaspforran
- Jastaal
- Jastus Farr's species
- Jatravartid
- Javelin
- Javkor's Species
- Jawa
- Jax the Conqueror
- Jazbinan
- Jedi
- Jeff (Men in Black)
- Jehetma
- Jekuul
- Jellien
- Jelly-bladder Plant
- Jellyblimp
- Jellyfish
- Jellyfloat
- Jelzap
- Jem'Hadar
- Jemat's Species
- Jempa
- Jenet
- Jenova
- Jentek
- Jerni
- Jerrilekan
- Jerroto
- Jesse
- Jetdarter
- Jevesect
- Jevon
- Jhazallan
- Jhef
- Ji'atrix
- Jigglypuff
- Jikiro
- Jillsarian
- Jilruan
- Jimmy (Jeff and Some Aliens)
- Jimvu
- Jinda
- Jinn (Jinnrise)
- Jinni
- Jiralhanae
- Jithna leaf
- Jitterbug
- Jo-adian
- John Silver
- Jokaero
- Jokhalli
- Jonathan Samuel Kent
- Joozian
- Jophur
- Jorenian
- Jostran
- Jotan
- Jotok
- Jotus
- Joustmite
- Jova's species
- Jovian
- Jovian (Destiny)
- Jovian (Doctor Who)
- Jovian (Not Final!)
- Jovian (Space Patrol)
- Jovian (Superinteressante)
- Jovian (The Jupiter Plague)
- Jowlpreener
- Jubba-Jubba
- Jubba Bird
- Jubilee Beetle
- Judge
- Judgementites
- Judoon
- Juggernaut
- Julian Sloane
- Julian deVascez's species
- Jumba Jookiba's Genetic Experiments
- Jumerian
- Junction Lizard
- Jungle Felucian
- Jungle Moon Arthropod
- Jungle Moon Ungulate
- Jungu
- Junior's species
- Junker
- Jupiterian Werewolf
- Jury Resplendent
- Justican
- Juzzian
- K'aarg
- K'aitian
- K'kart
- K'la'bisian
- K'lor'slug
- K'n-yanian
- K'oh Kajanian
- K'tang Kaktorri
- K'yipsas
- K-Series
- K-Tron
- KCO2
- Ka'hren
- Ka-Ma
- Ka Anor
- Ka Po' Tun
- Kaadu
- Kaalium
- Kabel1 alien
- Kabieroun
- Kablat
- Kaboot
- Kadmier
- Kadrians
- Kaernk
- Kaferian
- Kafit
- Kafkarian
- Kaftid
- Kagle
- Kago
- Kagouti
- Kaguya
- Kahler
- Kahler-Tek
- Kahori
- Kai Tok
- Kaidan
- Kaiju
- Kaiju (Pacific Rim)
- Kaiju (The Troop)
- Kaiju Skinmite
- Kairos Insectoid
- Kakaru
- Kakliosaur
- Kakori Punctatus
- Kakureimo
- Kal'Tik'Ma
- Kal-taar
- Kalaanite
- Kaldane
- Kalderan
- Kalduu
- Kaled
- Kaleesh
- Kalgeros
- Kalifadik
- Kaliman Retriever
- Kalincha
- Kalish
- Kalkar
- Kallidahin
- Kallusian
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