Nebula is a major character of the Marvel Cinematic Universe. She is the secondary antagonist of Guardians Of The Galaxy, a major anti-hero of Guardians Of The Galaxy Vol. 2, a supporting character of Avengers: Infinity War and a titular major protagonist of Avengers: Endgame, with her past version serving as the secondary antagonist of the latter. An alternate variant of her appears in the What If series as a major character of "What If T'Challa Became A Star-Lord" and a minor character of "What If Thor Were An Only Child". She is an adopted daughter of Thanos and former member of the Black Order, adoptive sister of Gamora (a Guardians of the Galaxy member), and one of two loyal enforcers of Ronan the Accuser (the other being Korath).
She is portrayed by Karen Gillan.
Guardians Of The Galaxy
Nebula first appears alongside Ronan, her former master. She witnessed the death of The Other, before her meeting with Thanos, her father. When Thanos wanted to obtain the Orb for unrevealed reasons, Ronan sent Gamora to retrieve the orb, but Peter Quill, a.k.a. Star-lord interferes with Gamora, both ending up in prison. Eventually, Gamora joined the Guardians, which left Nebula as Ronan's only enforcer (with the exception of Korath).
Sometime later, Drax, one of the Guardians, contacted Ronan while insane, which Ronan quickly came to Knowhere, searching of who made the call. When Ronan found out it was Drax, he dealt with him while Nebula was in search of the Orb. She made an attempt to kill Gamora, but Star-Lord saved her in time. Nebula was able to retrieve the Orb. They eventually learned that the Orb held an infinity stone, Ronan was going to give it to Thanos, but instead, he betrays Thanos by keeping it to himself, intending use it to destroy Xandar himself before destroying Thanos himself. Out of spite against Thanos for favoring Gamora, Nebula offers to help Ronan destroy a thousand planets in exchange for killing Thanos.
Nebula was still following orders from Ronan to destroy Xandar, which they were planning to destroy with Ronan's behemoth ship. The Guardians, with the help of the Nova Corps, eventually stormed through Ronan's ship and dealt with Korath, who was killed by Drax. Gamora was sent to open a door, but Nebula was sent to defend. Gamora and Nebula had a swordfight during when Ronan was trying to annihilate Xandar. Gamora got the winning hand and cornered Nebula to a cliff on Ronan's ship. Nebula let go and fell to her presumed death. Nebula, however, landed on one of the Ravager attack quads and tried to attack. She then escaped the war and left Ronan's side. She was never seen again in the film.
Guardians Of The Galaxy Vol. 2
Before the event of the film, Nebula infiltrated the planet of the Sovereign and attempted to steal some of the Souvereign's energy batteries. However, she was captured and imprisoned by the Sovereign high priestess Ayesha until the Guardians of the Galaxy arrived at the Sovereign planet and offered to battle the Abilisk in exchange for Nebula. After the beast is killed, Ayesha keeps her word and delivers Nebula into Gamora's custody. On their way back to Xandar, where Nebula is to be imprisoned, their spaceship crashes. While most of the team travel on with their newfound ally, Ego, Rocket and Groot remain in the wreck to guard Nebula.
However, when the Yondu Ravager Clan turn up to capture the Guardians, Rocket runs off to meet them in battle. While he is gone, Nebula manages to convince Groot to free her so that she can help Rocket. However, once she had been freed, she immediately betrays Groot. After Rocket has been captured by the Ravagers and Yondu refuses to assist in murdering the Guardians, a mutiny (led by Taserface) ensues. Nebula turns up just in time to witness the beginning of the mutiny and assists the mutineers by shooting the fin from Yondu's head with which he controls his telepathic arrow. She also blasts her gun at Rocket, electrocuting him.
With Taserface now leading the Ravagers, Nebula sets off with them in their spaceship. However, after advising Taserface and his men to deliver the Guardians and Yondu to the Kree for maximal payment, she decides to set off on her own in order to kill Gamora and to track down and murder Thanos afterwards. Kraglin Obfonteripresents her with a spaceship and Nebula leaves the Ravager-base. In her spaceship, Nebula returns to Ego's planet. There, she spots Gamora siting alone in a field.
She immediately heads her spaceship towards Gamora and starts firing. Gamora avoids being hit by jumping over a cliff but Nebula turns her ship around again and again, continuously shooting lasers at Gamora. Nebula even continues following Gamora when Gamora flees into a cave, causing the ship to crash as the cave is to narrow for its wings. This gives Gamora the oppurtunity to fire back, destroying the ship and trapping Nebula in the burning wreckage. Gamora pulls her sister out of the wreck seconds before it explodes.
Although both women are weakened, Nebula continues attacking Gamora until she eventually overpowers her and is able to draw a knife. However, she is unable to go through with murdering her sister and drops her. Nonetheless, she claims that she won and finally bested Gamora in combat, refering to the fights Thanos had them both fight when they were young. She spitefully confronts Gamora with the fact that Thanos forcefully turned her into a cyborg, ripping out her body parts piece by piece only because Gamora was unwilling to let herself get defeated in their battles. She then claims that all she was wanted back then was a sister and that Gamora was all she had.
The two then try to get back to the surface, but while they walk they suddenly find a chamber deep inside the planet, filled with corpses and skeletons. They realize that Ego is up to no good and even Nebula joins the team in attempting to defeat them. While doing so, Nebula and Yondu manage to destroy the Sovereign fleet hunting the Guardians. During the final battle against the living planet, Nebula even saves Gamora's life.
Avengers: Infinity War
Nebula returns in Infinty War, where she is kidnapped and tortured by Thanos, who is very disappointed in her for her betrayal against her. After collecting three of the Infinity Stones, Thanos kidnaps Gamora and forces her to reveal the location of the Soul Stone (the planet Vormir) by threatening to torture Nebula more. After Gamora gives out the location, Thanos leaves Nebula behind while taking Gamora to Vormir, where he reluctantly kills Gamora to get hold of the Soul Stone.
Nebula eventually escaped from her confinement and contacted the other Guardians to meet her at the planet Titan, where they meet up with Tony Stark, Peter Parker and Stephen Strange. However, Thanos arrived to the scene as he plans to collect the Time Stone from Strange. Though the heroes were briefly able to subdue Thanos, Nebula soon learned in horror that he killed Gamora to take hold of the Soul Stone. This provoked an angry Quill to attack Thanos, but the latter managed to beat them all before forcing Strange to surrender the Time Stone.
After collecting the Mind Stone from Earth, Thanos used the power of all six Infinity Stones to wipe out half of the universe's populace. Though Nebula has survived Thanos' slaughter, she is horrified to see Quill, Drax, Mantis, Parker and Strange perish away to their deaths, leaving her and Stark as the only survivors left in Titan. This made both a distraught Nebula and Stark realize that Thanos has finally accomplished his goal as the latter is last seen watching a sunrise from another planet.