Extraterrestrial life is defined as life that does not originate from Earth. It is often also referred to as alien life, or simply aliens (or space aliens, to differentiate from other definitions of alien or aliens). These hypothetical forms of life range from simple bacteria-like organisms to beings far more complex than humans.
The development and testing of hypotheses on extraterrestrial life is known as exobiology or astrobiology; the term astrobiology, however, includes the study of life on Earth viewed in its astronomical context. Many scientists consider extraterrestrial life to be plausible, but there is no conclusive evidence for its existence. Since the mid-20th century, there has been an ongoing search for signs of extraterrestrial life, from radios used to detect possible extraterrestrial signals, to telescopes used to search for potentially habitable extrasolar planets. It has also played a major role in works of science fiction.
Some aliens are friendly, but others are not.
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Makino (Max Steel) -
G-Man -
Tsubasa Yuunagi -
Gargantuan Leviathan -
Daisy Johnson -
The Iris -
Kirby -
Strike (OK K.O.! Let's be Heroes)
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- Aayla Secura
- Abauta of the Research
- Abeloth
- Absolute Tartarus
- Abzorbaloff
- Acastus Kolya
- Ace Hardlight
- Ace Killer
- Acklay
- Acumen
- Adam Power
- Addison Wells
- Adel (Kamen Rider)
- Admiral Atticus Noble
- Admiral Evar
- Admiral Han'Gerrel
- Admiral Malkor
- Admiral Razorbeard
- Admiral Shala'Raan
- Admiral Trench
- Admiral Zaal'Koris
- Adrien Victus
- ADVENT Trooper
- Aeos
- Aera (Fayelon)
- Agent of Demon Lords
- Agent Titan
- Aggregor
- Aggregor's soldiers
- Agi (Fantastic Children)
- Agito
- Aguilera (Kamen Rider)
- Ahdar Ru'afo
- Ahkmou
- Ahsoka Tano
- Ai Enma
- Aja Tarron
- Akane Shinjo
- Akila Theoris
- Akyanba
- Albedo (Ben 10)
- Alberich
- Alexandrite
- Alexis • Kerib
- Alien (Red vs. Blue)
- Alien (The Invasion of the Scooby Snatchers)
- Alien Akumania
- Alien Babarue
- Alien Baltan
- Alien Barossa
- Alien Bat
- Alien Boze
- Alien Bunyo
- Alien Cannan
- Alien Empera
- Alien Godley
- Alien Godola
- Alien Guts
- Alien Hipporito
- Alien Icarus
- Alien Kettle
- Alien Lasesta
- Alien Magma
- Alien Mefilas
- Alien Metron
- Alien Mijir
- Alien Miracle
- Alien Nackle
- Alien Neril
- Alien Pegassa
- Alien Pitt
- Alien Rayblood
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- Alien Sran
- Alien Stingers
- Alien Temperor
- Alien Tigers
- Alien Valky
- Alien Varduck
- Alien Zarab
- Aliena
- Alister Azimuth
- Allen the Alien
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- Allo
- Almighty Tallests
- Alpha Q
- Alphaman
- Alvan
- Amanita
- Amara
- Amate (Ultraman)
- Amelia Jones
- Amon (Starcraft)
- Anchorage Water Demon
- Andromedon (XCOM 2)
- Angelica (Battletoads)
- Animus (Power Rangers)
- Annihilation Wave
- Annihilus
- Anooba
- Ansaksie
- Anti-Pops
- Antlar
- Antlion
- Antonio (Ben 10)
- Antrax(TMNT-80)
- Anubias
- Anubis (Stargate SG1)
- Anubis Doggie Cruger
- Aparoids
- Aphoom-Zhah
- Apophis
- April O'Neil (2012 Version Series)
- Apros
- Aquamarine
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- Arachnid Bug Aliens
- Archimedel
- Archon Tahril
- Argit
- Aria T'Loak
- Aribunta
- Arisia Rrab
- Arkkis Chummuck
- Arlen Crane
- Armaggon
- Armus
- Aryana Mendez
- Aryana Westcott
- Ash Graven
- Asha
- Ashton Anchors
- Astal
- Astra
- Astra (Ultra Series)
- Astra Torch
- Asumi Fuurin
- Atalan Jackal
- Atriox
- Atrocitus
- Atropos (Kamen Rider)
- Audrey II
- Aunete (Pretty Cure)
- Aurico
- Aurra Sing
- Auta Magetta
- Autobots
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- Auton
- Aximili-Esgarrouth-Isthill
- Azald
- Azmorigan
- Azu (Kamen Rider)
- B'dg
- Ba'al
- Babidi
- Baboo and Squatt
- Bad Blood Predator
- Badonna
- Badoon
- Bagorah
- Bajillia Naire
- Balam Alliance - Sith Empire Enslaved Factions
- Balem Abrasax
- Bangray
- Banshee
- Baraba
- Barb Mentir
- Barbie
- Barby Koala
- Bardock
- Barodius/Mag Mel
- Baron Leltoy
- Barraki
- Barriss Offee
- Battle Beast
- Baz-El
- Beast (Tobot)
- Beast the One
- Beat Monsters
- Beheaded Kamikaze
- Beheeyem
- Behemecoatyl
- Bello
- Belzeus
- Bemstar
- Benglo
- Berg Katse
- Beroba (Kamen Rider)
- Berserker Alien ( Super Predalien )
- Berserker Predator
- Betty Barrett
- Bib Fortuna
- Bibimba
- Big Brain
- Big Horn
- Big Trail
- Bigs