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Can creatures be evil? Can they have malicious intent and a will toward domination? Or are they just the tools of others? Welcome back to ‘Sympathy for the Devil’. This time: Metroids
Cover of the NES game Metroid
Have you ever wondered why the game series is called Metroid? After all, it seems to be all about Samus and not the creatures known as metroids, right? They are the frequently difficult to defeat “enemy characters” but not even the main antagonists. They are constantly being used by one species or another and are feared throughout the galaxy – Super Metroid opens with "The last Metroid is in captivity. The galaxy is at peace."
Let’s review their tortured history.
The Chozo created them to be the "ultimate warrior". Having settled on SR388, the Chozo discovered the X parasite and, thinking them a potential threat to all life in the galaxy due to their ability to copy DNA and abilities of their victims, went about creating a creature to stop this threat: metroids (Metroid Fusion). The metroids were engineered to adapt to their surroundings, seek out “life energy” and propagate however possible (Metroid Prime 3: Corruption). To combat one possible galactic threat, the Chozo created another.
Hundreds if not thousands of years pass and the metroids fight back the X parasite to near extinction. The Galactic Federation comes across the metroids on SR388 and, not knowing anything about them, captures some for study. Enter the Space Pirates and Samus Aran.
The Space Pirates take the metroids and, seeing their immediate use as possible bio-weapons, begin to experiment on them.
Samus Aran’s home of K-2L is attacked by Ridley and the Space Pirates. Thinking they have killed everyone, they loot what they want and then leave. The Chozo arrive and find that only a three-year-old Samus has survived. They take her, give her some of their DNA and train her to be a warrior (Metroid Prime, Metroid Fusion and Metroid: Zero Mission). 
Knowing the Chozo’s modus operandi of creating one threat to combat another, is it not inconceivable that they took Samus and changed her biology in order to fight the metroids?
Throughout Metroid Prime and Metroid Prime 3: Corruption, the metroids are experimented on by combining their biological impulses toward leeching “life energy” with the mutagenic powers of phazon, a highly radioactive energy source with awareness if not possible sentience. Again and again, they are used as the tools for the Space Pirates resulting, at the end of Metroid Prime, in the creation of one giant prime metroid that, combined with the infection of Samus Aran’s power suit by phazon, results in the creation of Dark Samus, the antagonist of Metroid Prime 2: Echoes and Metroid Prime 3: Corruption.
A metroid, as seen in SNES game Super Metroid
The metroids are not evil, only engineered. Not unlike all other creatures, they seek only to survive and help their own kind. This is why a baby metroid, thinking the first thing it sees is its mother, imprints on and then later helps Samus in Super Metroid (as hatched in Metroid II: Return of Samus). Later, it is that same metroid’s DNA that helps Samus ultimately defeat the X parasite trying to escape from SR388 during the events of Metroid Fusion.
Of all the creatures in their universe, they are the most hated, feared and regarded with instant suspicion. It could even be argued that Samus was trained and transformed by the Chozo for the singular purpose of eradicating them. The Chozo created them as weapons, the Space Pirates experimented on them and the Galactic Federation dissects them. They lack a true home world, purpose and are ultimately driven to extinction by Samus. Did they ever really stand a chance?