The controlling entity inside the mothership of the invading forces, and final boss of the original Gradius. It is referred to as the mother computer in Gradius Rebirth. A parody of this boss was later used in Parodius Da!.

Its weak spot is the structures holding the Brain in place.

Attack Pattern

  • Gradius:

It's one and only in-game action is to close the entrance hatch on you. It self destructs in 30 seconds if that counts. The player might also ram the thing by accident.

  • Gradius Rebirth:

It gained the new ability to send Option Hunters at you. And not much else.

  • Nemesis ZX Spectrum Port:

In this port it attacks you firing four bullet at time in your direction. That may need a second to sink in.

  • Commodore 64 Port:

As with the Spectrum version, the boss now attacks you. but the bullets he fires are reduced into two.
This version also has the highest health of any boss in the game and Unlike the other variations of this boss - the weakspot in this battle is the brain itself.

Xaerous Brain an unevolved Bacterion?

There has been speculation Xaerous Brain may be a form of Bacterion himself. Such facts as Xaerous being the first Bacterian mothership, the story of Gradius III mentioning the rebirth of Bacterian and Bacterion's speech in Gradius III about how he "will always be reborn" may be evidence that the Brain is Bacterion. Another fact that may create a connection between the two is that the Brain is also known as Bacterion.


This "boss" established the series long running in-joke of having the final enemy be an absolute pushover. In this case, it does not attack at all.


Xaerous Brain appear in the Salamander second series. But unlike the game he originated from, he attacks.


Ships Vic Viper
Stages VolcanoStonehengeMoaiReverse VolcanoWasteland (PCE) • TentacleCellBase
Sub Bosses VolcanoZub RushMother and ChildIron MaidenTentacleElectronic Cage

Re-Bone (PC Engine) • Tornado (MSX) • Tyran Pace (MSX)

Bosses Big CoreCell NucleusXaerous Brain
Gradius ReBirth
Characters James Burton (Vic Viper) • GaudieVenom
Stages Stage 1Stage 2Stage 3Stage 4Stage 5
Bosses VolcanoIron MaidenBig Core DuoZub RushCrawler XMoai OrbRe-BoneEnigmaElectronic Cage MK2Xaerous Brain
End Bosses & Major Enemies
Major Recurring Foes GoferBacterionDr VenomZelos Force (Zeros)Lars Empire
Minor Enemies Xaerous BrainO.V.U.M.Eleos BrainMother Computer ZGuardian CoreCentral ServerGenocide CoreMetal SlaveZelos BarrierDoom