The Bacterians, or Bacterian Empire are the main antagonists of the Gradius universe. They are a mutant alien force which threatens the whole universe with their huge arsenal of mechanical and organic beasts. Their main leader is Bacterion, but they have also been led by Gofer and Dr. Venom. They cruise the universe in large battleships from the size of a planet, controlled by Gofer's mind, with his brain connected with the ship by organic wires. One of these ships is controlled by a huge brain made from Bacterion.
The origin of the Bacterians is unknown. Their main homeworld is planet Bacterian, which is actually a living being that is Bacterion himself, connected with Bacterion at it's core. Because of this, each time it's destroyed a piece that remains from it can regenerate and form a new planet Bacterian. The Bacterians can also infect other planets and mutate them into organic fortresses.
The Bacterians set their eyes in the planet Gradius, who poses their main threat, due to their highly advanced defense forces, composed by enhanced spaceships, especially one named the Vic Viper, who was responsible for their defeats. Dr. Venom is a traitor from planet Sin, an ally of Gradius, who allied himself with the Bacterians for revenge.
Small battleships: The Bacterians have a variety of small battleships, used for primary defense. They usually work in groups, due to their low defenses. Some are unable to attack, while others can shoot continuously and even warp themselves for kamikaze attacks on the enemy.
- Turrets: Placed in key spots, these immobile guns usually have a high fire ratio, making it difficult to dispose of them. Some of these, called Duckers, are capable of moving, which makes them even more annoying.
- Organic creatures: The bacterians can infect any living being to create their twisted specimen. From plants to animals and even lower lifeforms, tiny or huge. Giant flowers, floating brains, large eyes, fire birds and any other kind of abomination is at their disposal.
- Core Warships: Some of the most feared battleships of the bacterian, equipped with lasers and sometimes mechanical attachments such as arms and cannons, their only weak spot is a little core on their center, protected by thick walls. They may vary in size and firepower, but their principle is always the same, destroy the core and the thing is gone. They are generally the final line of defenses.
- Moais: The huge Easter Island statues, they form a formidable threat. They only weak spot is their mouth, from which they shot dozens of ripples in sequence. Their defenses are high, as well as their power. They vary in size and colors, some being able to multiply themselves or regenerate after being destroyed.
- Gunwalls: These are fortified walls made inside the bacterian fortresses serving as the last line of defense. They are powered up by cores, being equipped with guns and usually aided by Duckers.
- Shadow Walkers: When everything else fails, the Shadow Walkers serves as the final defense inside the bacterian ships. They are indestructible and can only be avoided by going under their legs, which is no easy task.
- Hive Minds: The Hive Minds are the commanders of the Bacterians. They usually have little to no attacks and are easy to destroy, but some Hive Minds can fight back.
- The leader is always located at either a fortress or a planet that the leader infects and transforms into a fortress.
- In each game, all the enemies you fight are controlled by the final boss. So in a sense, you are fighting the final boss this whole time.
- The Bacterians are known for adapting to several situations, as shown in the Cell levels.
- The Bacterian possesses the ability to mainpulate matter.
- The energy cores in core warships are control interfaces and also power sources.
- When a Bacterian lifeform is born, it starts as an organic clump. When it's fully grown, it looks completely mechanical.