Spoiler warning:The following contains key plot or intense ending details.
Leviathans (also known as Leviathan Seeds) are large, sentient asteroids originating from the planet Phaaze. The Leviathans are made of large concentrations of Phazon. When they impact a planet, Phazon is introduced to the ecosystem, mutating inhabiting creatures with the effects of Phazon.
The sole purpose of the Leviathans is to initiate the spread of Phazon throughout targeted planets and convert them into clones of Phaaze. Every planet encountered in the Metroid Prime series (with the exception of those encountered in Metroid Prime Hunters) is attacked by a Leviathan.
Leviathans begin their life cycle as an Infant Leviathan, found only in the deepest regions of Phaaze. They bear a small resemblance to Infant Tallon Metroids in size and movement. The infant is unable to attack Samus but produces a toxic gas on the surface of the ground beneath it, which deals a great deal of damage over time. The infant can only be attacked and destroyed by ripping off the excess Phazon growth on the womb via the Grapple Lasso surrounding the Infant Leviathan. The X-Ray Visor can be used to get a definite lock on the creature. Once the infant is targeted, Samus must then use her Nova Beam to damage the infant's weak points as the infant alternates between the two sides of the areas in which Samus ripped off the excess Phazon growth. Once the infant is terminated, Samus must continue down into a large room and confront Dark Samus.
Tallon IV Incident
- Main article: Tallon IV
Samus first encounters Phazon and a Leviathan's work in Metroid Prime decades after the Tallon Leviathan lands.. The meteor landed on Tallon IV, spreading Phazon (known to the Chozo as the "Great Poison") throughout its various ecosystems. The Chozo were helpless against the corruptive power of Phazon and could only watch its raw, destructive nature in action. Phazon spread, corrupting or killing anything in its path. Phazon attacked any living creature and plant, corrupting even the Chozo, turning their dead to Chozo Ghosts. These Chozo Ghosts only fiercely protected their land, attacking any, even former friends, who would approach. Despite this, The Chozo did not simply flee the planet. They sealed the Leviathan's Impact Crater away using the Artifact Temple. They placed the temple directly above the impact site and sealed it with twelve keys, hoping that one day the foreseen "Entrusted One" would unlock the temple and purge the Phazon inside. The temple additionally protected evil from obtaining Phazon for selfish use.
After the Chozo sealed the impact crater and either fled Tallon IV or fell to Phazon corruption, Samus arrives on the planet after chasing down the enhanced space dragon Meta Ridley from Frigate Orpheon, from whence she receives a distress signal, presumably from Pirates as Orpheon was attacked by the creatures within. After investigating the planet, Samus learns that Space Pirates were using Phazon with Metroids and other creatures to create formidable bio-weaponry. It then becomes her mission to destroy Phazon on the planet. She achieves this by finding the twelve Chozo Artifacts and opening the Artifact Temple. Although there is no Leviathan within the core, it is assumed that the creature Metroid Prime had taken on its role as the source of the planet's Phazon. Samus enters the Impact Crater and defeats Metroid Prime using her Phazon Suit and Phazon Beam, overloading the creature.
It is known that the creature Metroid Prime is somehow connected to Leviathans. By defeating it, the Phazon threat in Tallon IV is eliminated. Additionally, the Genesis Chamber in Corruption contains a husk of Metroid Prime. It is unknown whether there is only one Metroid Prime and the husk was shed or if there are multiple Primes and this husk belongs to one of them.
- Main article: Aether
Fifty years before the events of Corruption, a Leviathan approached the planet Aether, home to the Luminoth. As it approached, the Luminoth detected it and attempted to destroy it, but failed. As it impacted, the Luminoth took refuge and accepted their fate as Phazon seeped from it, corrupting the planet. A Leviathan struck the Luminoth's planet Aether, forcing it to an unstable state and splitting it to two planets, Aether and its "dark twin", Dark Aether. With the creation of Dark Aether came the Ing, destroying much of Aether and the Luminoth. Because a Leviathan landed on the planet, Dark Aether contained high levels of Phazon Ore, attracting Space Pirates to investigate. Pirates extracted as much Phazon ore as possible for weapon purposes.
The Galactic Federation becomes aware of the presence of Leviathans on several planets in Metroid Prime 3: Corruption and sends three bounty hunters to destroy the seeds. Dark Samus manages to corrupt and control these bounty hunters: Rundas, Ghor, and Gandrayda. She then assigns them to defend the Leviathans on Bryyo, Elysia, and the Pirate Homeworld, respectively, from Samus. Dark Samus even manages to corrupt an Aurora Unit, AU 313, to protect the planet Phaaze. Dark Samus and the Space Pirates seek to harvest the Phazon-spewing Leviathans for their corruptive and destructive power (ironically, Leviathans are their undoing, as Samus uses one to reach the planet). All known Leviathan seeds, however, are destroyed by Samus, along with their parent planet Phaaze.
- "Planet Tallon IV, formerly a Chozo colony, was struck by a stellar object 50 years ago. Object was later determined to contain large quantities of Phazon. The Chozo were able to stave off the spread of Phazon, at the cost of many Chozo lives. The survivors abandoned the planet, fleeing to an unknown location. Decades later, Hunter Samus Aran responded to a distress call in the sector and discovered a Space Pirate Phazon Mining Station there. Aran eliminated both the pirate and Phazon threat from the planet, though not without cost." —GF Data - Tallon IV Incident (Metroid Prime 3: Corruption)
- "Unforeseen by sages, a meteor came as if from nowhere, casting a dark shadow of debris over the land with the violence of its impact. Its destructive force spent, the fallen star burned itself out rapidly, and the incident should have faded into memory...but the meteor brought with it corruption. A Great Poison burst forth into the land, a strange energy that clawed at natural life with a ferocity that seemed almost sentient. Bound by our ignorance of this phenomenon, we Chozo could only watch in horror as this dark force slowly began to spread across the surface of Tallon IV." —Chozo Lore - Meteor Strike (Metroid Prime)
- "As the Great Poison reaches ever further into the planet, we Chozo begin to feel the gnawings of despair - before it is too late, we now make our last stand. We have begun to build a temple to contain this darkness; at its heart we will place a Cipher, a mystical lock powered by twelve Artifacts and filled with as much power as we Chozo can harness. We wonder, though - even when we are done, will it be too late? And will the power of the temple, and the Cipher itself, prove strong enough to hold back the poisonous tide that even now swells within the ground, threatening all life?" —Chozo Lore - Cipher (Metroid Prime)
- "To the Entrusted One: if you read these words, then our hope has not been in vain. Your path is fraught with danger - monstrosities beyond description lurk in the shadows, starving, hunting for prey, searching for ways to quench the poisonous urges that bloom in their brains. Some of these are shrewd, but they are blinded by their evil designs: believing in the black promise of the Great Poison, they seek to harness it for their own ends. It is these last that are the greatest danger, perhaps an ever greater one than the Great Poison itself. When you rid the universe of these creatures, you will be the true Entrusted One." —Chozo Lore - Infestation (Metroid Prime 3: Corruption)
- "By the time we detected the stellar object as it streaked toward our world, it was too late to stop it. We fired numerous weapons at it in a vain attempt to alter its trajectory. Nothing worked. Our efforts placed a great strain on the Energy Controllers, and weakened Aether. All we could do as the object drew closer was take shelter and wait. We gathered stores of food and water, reinforced the shielding on our dwellings, and spent the last hours in peace." —Luminoth Lore - The Stellar Object (Metroid Prime 2: Echoes)
- "Planet Aether, home of the Luminoth, was struck by a “Phazon Meteor” five decades ago. The impact had catastrophic effects on the already unstable planet, creating a “dark twin” of the planet and a fierce race known as the Ing. A brutal war between the twin planets took place, with the Ing gaining the upper hand. The G.F.S. Tyr went to the sector to investigate pirate activity, but were forced to make an emergency landing on Aether. Shortly after, the entire crew of Tyr was attacked and annihilated by the Ing. Hunter Samus Aran was sent to investigate, and wound up entangled in the local conflict. Aran fought against both Space Pirates and Ing, and arose victorious. Aether’s “dark twin” vanished, taking with it the Ing horde, and the planet’s peace was finally restored. After the Aether incident, the Federation sent the G.F.S. Anhur back to Aether to deal with the pirate base. Upon arrival, the crew and marines of the Anhur assisted the native Luminoth in dismantling an abandoned Space Pirate mining facility. During the operation, the crew detected the presence of Phazon. The ship’s crew investigated and collected several kilograms of ore, which would later lead to the development of the PED." —GF Data - Anhur Incident (Metroid Prime 2: Echoes)
- "Leviathans are the children of Phaaze. They are bioforms that begin life deep within the planet, inside the base of a serpentine organ that serves as a womb. The Leviathan will remain in here, feeding on endless supply of Phazon, until it has developed its Phazon core. The developed core marks the Leviathan's transition into adolescence and its departure from the womb. The serpentine organ moves the adolescent from deep inside Phaaze and releases it closer to the planet's surface. Here the bioform will continue to grow and mature underneath its older siblings. As time passes and the older ones are launched into space, the Leviathan will slowly make its way to the planet's surface. It is here the Leviathan will reach full maturity. Once Phaaze has located a planetary target to corrupt, it will launch the Leviathan into space. The Leviathan is capable of interstellar travel, creating wormholes in space to expedite the journey. Instinctively, it homes on its planetary target. Shortly after impact, the bioform dies, leaving its armored shell to protect the Phazon core. Before it dies, the bioform often attracts and enthralls a large local predator. After mutating it through intense Phazon exposure, it compels the creature to protect the core. The core then begins to seep into the planet, replacing the local ecosystem with one based on Phazon." — Logbook "Leviathan Infant" (Metroid Prime 3: Corruption)
- "Serpentine organ serves as a Leviathan womb. Tissue on the sides looks like it could be torn off." —Scan Data (Metroid Prime 3: Corruption)