The Queen Metroid is the final form of a Metroid's life cycle, as well as the largest and most powerful variant of the species.
Only two Queen Metroids have appeared chronologically in the Metroid series; the first Queen appears as the main antagonist and final boss of Metroid II: Return of Samus as well as its remake Metroid: Samus Returns. A second Queen, born out of cloning from an offspring of the first, appears in Metroid: Other M as the penultimate boss (third to last if counting Phantoon in the epilogue).
The Queen shares the structure to a crocodile or tetrapod dinosaur, as she has a long snout filled with sharp teeth and crawls on four legs. She has two pairs of four blue eyes, armored platings on her back, and a translucent belly. Similarly to other Metroids, her weak points are her head, mouth, and stomach, which the latter can be damaged by Bombs or destroyed by a Power Bomb from the inside. Much like an ant or bee colony, the Queen Metroid reproduces the entire species, and only a few Metroids are born with the specified genetic coding to eventually mutate into a Queen. The Queen does not appear to require a mate to create descendants, making her (and likely the entire species) parthenogenetical.
In Metroid: Samus Returns, the Queen's appearance is slightly altered, giving her an armored carapace, side jaw flaps, ten red eyes, spikes on her forelimbs, and a tail, which she lacked in previous games. Her uvula also has a more spike-like shape, making it more noticeable when using the Grapple Beam on it.
Much like the rest of the species, the Queen Metroid is a destructive parasitic predator that desires to kill anything in sight, although she shows a more noble side for the protection of her offspring, given how she's the only member of the species who would nurture the young. Because of this and the fact that only one Queen can exist in a nest at a time, her hostility is extreme compared to other Metroids, as she is willing to slaughter or devour any living being that stands in her way of protecting her offspring. The Queen is also willing to kill other Metroids, even her own children.
During Samus Aran's mission on SR388 to eradicate all of the Metroids to prevent them from endangering the universe, the Queen Metroid was the last Metroid left for Samus to terminate, located in the deepest confine of the cavern complex of the planet. After killing the Queen, Samus witnesses the birth of the last Metroid egg, but kept it with her as she left the cavern.
Metroid: Samus Returns
In the remake of Metroid II, Samus once again locates the Queen Metroid resting in the deepest corridor of SR388 and engages it in a fierce battle to kill off the Metroids for good. In this game, more of the Queen's abilities can be seen, as she is able to spew out a red laser beam and green clots of poisonous gas from her mouth, with her eyes changing to bright red or green to indicate which one she is about to fire out. She is also able to breathe out a large amount of air in attempt to blow Samus into a wall of fire caused by the laser or into the poison gas. Occasionally, the Queen will attempt to bite Samus, but at the right sync, Samus can Melee Counter the Queen's attack and use the Grapple Beam to open the Queen's Mouth, allowing her to fire into the Queen's mouth, or enter said mouth using the Morph Ball and use a bomb or Power Bomb within the Queen's stomach. As with all of the other Metroids in the game, the Queen disintegrates upon death.
Oddly, even though Samus Returns is a remake of Metroid II, the Queen is not the final boss of the game, as that title goes to Proteus Ridley, who is fought as Samus makes her way back to her ship with the Baby Metroid.
Metroid: Other MDuring the events of Metroid: Other M, Metroids were cloned from fragments of the Baby Metroid on Samus's suit after it was killed by Mother Brain in Super Metroid, and propagated in Sector Zero of the BOTTLE SHIP. The first cloned Metroid matured into a Queen, meaning that the Baby was actually an infant queen. The Queen, along with all of the other Metroids, were nurtured by MB, an Android built with the information and personality of Mother Brain. The Galactic Federation left the Queen's genes unaltered so she would produce normal Metroids for the Federation to conduct experiments on.
Though not fully seen until her boss fight, the Queen's presence can be hinted in the cutscene where she killed Ridley's clone when it ventured too close to her chamber and absorbed its life force, as well as some of its powers, including Ridley's signature fire breath.
Samus comes across Room MW, and finds Madeline Berman in the next room through a glass window. Madeline mistakes Samus as an agent sent to assassinate her and in a panic, opens the Queen's chamber. When Samus ventures inside, she finds hatched Metroid eggs, and immediately realizes the presence of the Queen Metroid as the latter appears right in front of her and roars.
The Queen deploys six Metroids (first one, then two, and last three) from small holes on her back and slams on the ground when Samus freezes the Metroids with her Ice Beam. Once all six of the Metroids are destroyed, the Queen grows crystalline spike platings on her head and neck and sprays a flammable breath at Samus. However, she seems impossible to beat as she grows a second planting once all of the first platings are destroyed. Samus, remembering the kind words of Adam and Anthony, uses Concentration and prepares to fire at the charging Queen, but is interrupted when the ship's emergency brakes activate, throwing them both on the ground. Samus takes the opportunity to shoot at the Queen's unprotected belly, and quickly enters the Queen's mouth via the Grapple Beam as she charges a powerful variant of her fire breath. Samus then allows herself to the use of Power Bombs to create a massive explosion from inside the Queen's stomach and obliterate the nucleus, thus killing the Queen.
- As the Metroid franchise was known to have taken inspiration from the Alien franchise, the Queen Metroid highly resembles the Xenomorph Queen, as both are able to reproduce the Metroid and Xenomorph species. In both Aliens and Metroid II, the final battle is between the queens and the lead heroines (Samus Aran and Ellen Ripley) and in Alien Resurrection and Other M, a queen is created via cloning.
- In Other M, the Queen's vision is blurred pink in the cutscenes where she kills Ridley's clone and spots Samus in her chamber. Also, a faint greenish glow can be seen around Ridley and Samus during these same cutscenes, presumably suggesting that Metroids, or at least the Queen, can sense their prey's life force.
- In Other M, If Samus is unable to fire enough missiles at the Queen's belly or grapple beam her way into the Queen's mouth in time, the Queen either bites or fires an unavoidable fire beam, both killing Samus instantly. She, Vorash, and Goyagma are the only bosses in the game capable of killing Samus in one hit.
- There are two tube-like appendages located at the rear of the Queen, referred to her tail in the Other M guide. While it is debatable what their function is as they are never shown in action, it is theorized that they are used as the Queen's organs for laying Metroid eggs, as her body lacks any other protrusion to serve that purpose. Each time the Queen from Other M smashes into a wall, strange green fluid squirts out from the two tubes. According to the guidebook of Other M, the liquid is considered "poisonous projectiles" erupting from the Queen's tail, although they have no effect on Samus in game.
- In Metroid II, when Samus kills all Metroids in a certain area, an earthquake occurs (replaced with the Chozo Seal in Samus Returns), lowering the lava level in a certain spot. Although debatable what the source for the earthquakes is, some players speculate the Queen Metroid as the source, stomping rapidly in fury for the deaths of her children. In both Metroid II and Samus Returns, the Queen can be heard roaring in the room before confrontation, mourning the loss of her Metroid offspring.