Species of the Marvel Cinematic Universe

The Marvel Cinematic Universe (MCU) is an American media franchise and shared universe centered on superhero films and other series starring various titular superheroes independently produced by Marvel Studios and based on characters that appear in American comic books published by Marvel Comics. The shared universe, much like the original Marvel Universe in comic books, was established by crossing over common plot elements, settings, cast, and characters. Due to the galaxy-spanning nature of the franchise, multiple species have been introduced.
Asgardians.
The Asgardians, or the Æsir, are the inhabitants of Asgard on which the gods of Norse mythology are based. They are a race of extraterrestrials similar in appearance to humans, possessing a highly advanced form of technology resembling magic and sorcery, which their entire civilization is built on. They are mainly wiped out by Thanos, Hela, and Surtur.
They appeared in the films "Thor", ', ', ', ' and "", through Thor in "The Avengers" and "Doctor Strange", and through Sif in the ABC series "Agents of S.H.I.E.L.D.".
Celestials.
Celestials are an ancient race of entities that possess vast matter and energy manipulation abilities. They were present long before the dawn of the galactic communities and even the Asgardians. Their origin and nature is shrouded in mystery. Whatever is known about them is known only by a few, such as Taneleer Tivan / The Collector, who reveals that the Celestials utilized the Infinity Stones as a means of power against lesser life forms. The severed head of a deceased Celestial was converted into Knowhere. The head appears in "Guardians of the Galaxy" and "Avengers: Infinity War". 
In "Guardians of the Galaxy Vol. 2", Ego the Living Planet, Star-Lord's biological father, is a Celestial who controls a humanoid avatar to travel the universe. His planetary form is a living extension of his Celestial consciousness. Over the course of many years, he planted thousands of alien-seedlings to expand his existence across all life sustaining planets. However, Ego needed another Celestial's assistance to activate them, so he fathered children with various alien races and had Yondu Udonta retrieve them so he could gauge their Celestial powers. Quill is the only child who gained his father's Celestial abilities, though he loses them after killing Ego and foiling his plans. Eson the Searcher is one of the previous owners of the Power Stone. He used its power to level the surface of an entire planet. The Celestials will appear in the upcoming film, "Eternals".
They appeared in the films "Guardians of the Galaxy" and "Guardians of the Galaxy Vol. 2", and through Quill in "Avengers: Infinity War" and "Avengers: Endgame".
Chitauri.
The Chitauri are a powerful, reptilian warrior race, a hybrid between organic beings and machines. They have a caste-like society, with each caste (nearly a different species in itself) fulfilling a different role in Chitauri society. They are in league with Thanos through his vizier, a hooded being called "the Other". They are presented as a race of grey-skinned, six-fingered reptilian humanoids that have a bio-mechanical physiology and superhuman attributes. Their technology ranges from hovercraft-like skimmers and Necrocraft, to living airborne troop carriers called Leviathans, all neurally linked with a mothership.
They appeared in the films "The Avengers", "Guardians of the Galaxy", "Avengers: Infinity War" and "Avengers: Endgame".
Dwarves.
Dwarves are an ancient race of skilled forgers and blacksmiths who hail from the realm of Nidavellir. They are ruled by King Eitri. They are close allies of the Asgardians, and after being asked by Odin, forged Mjolnir.
Eitri appears in "", when Thor, Rocket, and Groot arrive on Nidavellir. They find Eitri who informs them that Thanos killed the rest of the Dwarves after they forged the Infinity Gauntlet.
They appeared in the film "Avengers: Infinity War".
Elves.
Elves are two separate races – Dark Elves (from Svartalfheim) and the Light Elves (of Alfheim). The Dark Elves, led by Malekith, first appear in "Thor: The Dark World". The Dark Elves, as with their enemies the Asgardians, are depicted as ancient astronauts. It is stated that they existed in the primordial darkness that predated the current vibrant state of the universe. Their goal is to destroy the current universe and return existence back to that state. They were believed extinct, but unbeknownst to the Asgardians, Malekith and a number of warriors escaped and went into stasis in deep space until another attempt would be possible. For the film, David J. Peterson created a language for the Dark Elves called Shiväisith. In "Guardians of the Galaxy", an imprisoned Dark Elf appears as an exhibit in Taneleer Tivan's museum. In "Spider-Man: Homecoming", Dark Elf technology that was salvaged from the Battle of Greenwich was used by Tinkerer alongside the technologies from the Chitauri and Stark Industries.
They appeared in the films "Thor: The Dark World", "Guardians of the Galaxy" and "Avengers: Endgame".
Eternals.
The Eternals are a race of superpowered beings, the result of experiments by the Celestials. They are the sister race to the Deviants. The Titanian Eternals were a technologically advanced race that perished due to overpopulation and lack of resources. They appear in the Marvel Cinematic Universe in the form of Thanos, an Eternal (albeit with Deviant syndrome) from Titan. The Eternals of Earth will be fully featured in the film "Eternals".
They appeared (through Thanos) in the films "The Avengers", "Guardians of the Galaxy", "Avengers: Age of Ultron", "Avengers: Infinity War" and "Avengers: Endgame".
Flerkens.
Flerkens are alien creatures resembling Earth cats in appearance and behavior. They have tentacles that come out of their mouths and can swallow up large objects and store them in pocket dimensions in their bellies. Goose, Nick Fury's pet, demonstrates this ability in "Captain Marvel", swallowing the Tesseract.
They appeared in the film "Captain Marvel".
Frost Giants.
The Frost Giants are the race of large humanoid beings that inhabit the frozen, barren realm known of Jotunheim. They are ruled by Laufey, king of the Frost Giants, who is also Loki's true biological father. Small and weak for a Frost Giant, Loki was abandoned by his father in a temple, and left to die. In 965 A.D., not long after the war between the Giants and the Asgardians, Loki was found by King Odin and raised as his son.
They appeared in the film "Thor", and through Loki in the films "The Avengers", "Thor: The Dark World", "Thor: Ragnarok", "Avengers: Infinity War" and "Avengers: Endgame".
Kree.
The Kree are a militaristic race of mostly blue-skinned humanoids from the planet Hala. One of the most technically advanced races in the galaxy, the Kree are skilled in genetic engineering and are responsible for the creation of the Inhumans on Earth.
First featured in "Agents of S.H.I.E.L.D.", they make their cinematic debut in "Guardians of the Galaxy". Ronan the Accuser and Korath the Pursuer are the only notable Kree individuals that appear in the film. The Kree Empire is stated to have just signed a peace treaty with the Nova Corps of Xandar, thereby ending a centuries-long war between the two races. This treaty prompts the radical Ronan to embark on a renegade campaign of genocide against all Xandarians. To the Nova Corps' frustration, the Kree Ambassador (portrayed by Tomas Arana) tells Irani Rael that the Kree Empire refuses to stop Ronan's killing spree and that his plot is not their concern as they have done enough with the peace treaty. The Kree briefly appear in "Guardians of the Galaxy Vol. 2", where their planet Hala is nearly destroyed by Ego. They next appear in "Captain Marvel". Pace and Hounsou reprise their roles as Ronan and Korath, and are joined by Yon-Rogg, Minn-Erva, Att-Lass, and Bron-Char, who are members of the Kree military team Starforce. Mar-Vell and the Supreme Intelligence also appear in the film. Yon-Rogg came to Earth when the Kree discovered that Mar-Vell was working on a light-speed engine experiment as well as harboring some Skrulls. When Mar-Vell died in a crash with Carol Danvers and Yon-Rogg arrived, Carol shot the engine and got exposed to its energies. After a blood transfusion from Yon-Rogg, Carol's memories were altered and worked under him and the Supreme Intelligence. Carol then arrived back on Earth following an encounter with the Skrulls led by Talos. When it came to a parley with Talos, Carol learned what the Kree did to the Skrulls and their homeworld. After getting the dampener removed from her head, Carol uses her powers to fight the Kree forces which resulted in most of them either being killed or incapacitated. Yon-Rogg was sent back to Hala to relay Carol's message to the Supreme Intelligence.
They appeared in the films "Guardians of the Galaxy" and "Captain Marvel", in the ABC series "Agents of S.H.I.E.L.D.", and through Danvers in the film "Avengers: Endgame".
Outriders.
The Outriders are mindless aliens utilized by Thanos in his army. The Outriders make their first live-action appearance in the Marvel Cinematic Universe film ', in which they invade Wakanda. Alternate versions of the Outriders appear in ' during the final battle, but are disintegrated at the end.
The non-canon novel "" gives their origin as the result of Thanos combining samples of DNA from the Chitauri, himself, and of various species that he has killed.
They appeared in the films "Avengers: Infinity War" and "Avengers: Endgame".
Sakaarans.
Sakaarans, also known as Sakaarians, are a sentient insectoid race native to the planet Sakaar. They first appear in "Guardians of the Galaxy", working for Ronan the Accuser as soldiers. A maskless member of the race is portrayed by James Gunn. A separate type, larva-like creatures, appears in ' and ', in the form of Miek.
They appeared in the film "Guardians of the Galaxy", and through Miek in "Thor: Ragnarok" and "Avengers: Endgame".
Skrulls.
The Skrulls are a race of extraterrestrial shapeshifters hailing from the planet Skrullos. 
They appeared in the films "Captain Marvel" and "Spider-Man: Far From Home", as well as the Disney+ series "WandaVision".
Sovereign.
The Sovereign are a golden-skinnned humanoid race that has advanced through genetic engineering and live on the amalgamation of planets of the same name. They are led by Ayesha, the Golden High Priestess. In a post-credits scene in "Guardians of the Galaxy Vol. 2", Ayesha oversees the birth of the latest member of the race—Adam, who she intends to use as a weapon against the Guardians.
They appeared in the film "Guardians of the Galaxy Vol. 2".
Other species.
Several other species make appearances throughout the MCU, often in the form of a single character. These include Xandarians (such as Kraglin and the Nova Corps), Kylosians (Drax), Luphomoids (Nebula), Flora Colossus (Groot), Zehoberei (Gamora), insectoids (Mantis), Krylorians (Bereet and Carina), Kronans (Korg), Korbinites, and Watchers.