Appearing sometime after the founding of the Fellowship approximately twenty years prior to the Astronomical Alignment, the Tetrahedron Generator served the function of disrupting the ethereal waves of Britannia, causing them to become sharp instead of smooth, thus making the arcane arts unreliable and driving many mages and wizards to madness as their natural attunement to the ether was corrupted.
Situated within the Dungeon Deceit, this blackrock construct could only be entered by a party possessing and wearing the enchanted Ethereal Ring - all others would fall into a deep slumber upon approaching it, only to wake up to find themselves elsewhere. Guided by the Time Lord and the seer Penumbra, the Avatar located this artifact and stepped inside the Tetrahedron, where they were forced to combat its spectral guardian. Once the hero slew the beast, the generator too was destroyed, and the Avatar was able to lay claim to the miniature Blackrock Prism which lay within it.
With its destruction, magic in Britannia returned to normal and mages regained their sanity.
|“|| The Tetrahedron generator is located in the room at the northeastern tip of Deceit. There is no puzzle here. All that is necessary - not to imply it is an easy task - is to defeat the ethereal monster. A magical weapon is required to harm it, a glass sword being the ideal choice in arms.|
- According to the Time Lord, the three blackrock generators were sent to Britannia from the Guardian's home-world; indeed, while developing Ultima VII, Richard Garriott envisaged Britannia's would-be conqueror to have originated from a race of omniscient, godlike entities who might themselves eventually become antagonists in the series. This, however, would later be superseded by Ultima IX, in which it is stated the Guardian coalesced out of darkness purged from the Avatar in the final moments of Ultima IV.
- The shapes of the three generators (a cube, sphere, and tetrahedron) form the logo used by Electronic Arts from 1982 to 1999. Richard Garriott has since given conflicting statements, both denial and confirmation, as to whether this was conceived as intentional symbolism.
- A lightning trap lies directly at the entrance of the Tetrahedron, although it can be disarmed using a standard Destroy Trap spell.
- It is possible to short-circuit the plot by squeezing your way past the moongate at the Sphere Generator, meaning that the Tetrahedron Generator isn't destroyed first. However, in order to destroy the Cube Generator, it still has to be destroyed.
- In the SNES Port of Ultima VII, the Ethereal Monster lies in the chamber directly before the Tetrahedron, although the Ethereal Ring is required to slay it. In addition to this, the Tetrahedron features no internal defenses, and will self destruct the moment the Avatar moves its corresponding prism from a nearby pedestal.
- Time Lord. Underworld Dragon's Ultima VII Transcript. Ultima VII. "ethereal defense, fix magic, tetrahedron".
- Penumbra. Underworld Dragon's Ultima VII Transcript. Ultima VII. "blackrock, protect, ring".
- Time Lord. Ultima VII Usecode. Ultima VII. "Cube, Sphere, Tetrahedron".
- DeMaria, Rusel et al. "A Conversation With Richard Garriott". Ultima: The Avatar Adventures. Prima Publishing: 1992. Pages 381, 388–389.
- Shamino. Quill Dragon's Ultima IX Transcript. Ultima IX.
- Kumar, Mathew. "The Making of Ultima VII: The Black Gate". PC Gamer UK. Future Publishing Ltd: December 2011. Page 154.
- Garriott, Richard. "Richard Garriott on Twitter". Twitter. 2014-03-03. Retrieved 2017-09-13.