E-106 Eta was commander of a Badnik Horde stationed near Spagonia, and was dispatched by Eggman to Spagonia University to capture Sir Charles Hedgehog and Professor Pickle. Successfully kidnapping the professors and their research data surrounding the Gaia Manuscripts, Eta transported them aboard an Egg Train in order to reach Bullet Station in the Rail Canyon Zone. However, the Knothole Freedom Fighters intercepted the train in an effort to rescue the captured professors. Eta was alerted to their presence after coming across NICOLE in her hologram form, and in its efforts to eliminate her destroyed the train's controls. Caring nothing for the train's dangerous acceleration, Eta continued to pursue NICOLE until her hologram form disappeared before traveling to intercept Sonic the Hedgehog in the car containing the two professors. (StH: #257, #258)
During the Freedom Fighters assault on Eggmanland, Eta one of the many Badniks that defended the facility. Although it put up a fight, Eta was eventually bought down by Bunnie with a single energy charged punch; while being held in place by Sally and Antoine. (StH: #286)
In terms of personality, Eta has displayed unwavering devotion to Dr. Eggman and thwarting the doctor's enemies. In this latter purpose it is notably single-minded, causing destruction despite the risk to captives and information valued by its creator.
Unlike most of its predecessors, E-106 Eta seems to have been designed primarily for melee combat. Instead of a single or dual laser cannons, its arms end with two large spikes, and the arms themselves are piston-like. As such, they are similar to the cyborg limbs of Matilda the Armadillo, and allow Eta to drive its spikes through various obstacles with relative ease.
- Eta was never formally introduced in the continuity that existed before the second Genesis Wave, but his fate was revealed in the (now defunct) Sonic Universe blogs.
- Originally E-107 Theta was intended to be the main villain of StH #258. However, due to Theta's connection with Light Mobius his role was instead to filled by Eta, according to Ian Flynn. A typo in #257 identified Eta as E-107, but this was corrected in later issues.
Eta is a large, gray-armored robot, its form reflecting a clear progression from the design of the early E-100s like E-103 Delta to E-123 Omega. The symbol for the Greek letter Eta, H, is incorporated into its shoulder design.