Eunice, otherwise known as the Unimatrix, is a living prototype Omnitrix created by Azmuth. She can absorb and contain DNA of various different species and use their abilities. She is a close ally of Ben Tennyson's team and currently works as Azmuth's assistant.
The Unitrix's pod was discovered in the forest at the same time Ben's team was driving for a camping trip. When Gwen cut her hand trying to open the pod containing the Unitrix, her DNA was sampled and randomized to make a human form for the Unitrix (explaining why Eunice has blond hair while Gwen has orange/red hair).
Ben and Eunice were soon attacked by Sunder, who shut Eunice down and attempted to leave Earth before Kevin Levin and Gwen Tennyson stopped him. Once Kevin restarted the Unitrix again, reawakening Eunice, the four of them scuffled with Sunder until Azmuth arrived and cleared things up.
Azmuth stated that Eunice was a prototype model of the Omnitrix called Unitrix, created when the Galvan acientift wanted to preserve alien DNA by placing genetic samples in individual Unitrixes that can animate themselves to take on the appearance, and use the abilities, of the DNA samples that were uploaded into them. Following a brief argument, Ben allowed Azmuth (under a compromise) to take on Eunice as one of his assistants on Primus.
Eunice has very similar functions to her successor, the Omnitrix (making her slightly akin to a living machine). However, her true form is an individual container that can only store one sentient DNA sample, which acts as her mobile or general form. In this case, her general form is an adolescent human, as Gwen was the first sentient life form to touch her pod.
According to Derrick J. Wyatt, since her DNA origin was Gwen, it would mean that Eunice is technically part of the Tennyson family. Furthermore, she is not truly Gwen's clone, as her DNA was scrambled extensively to make it very different. Therefore, the DNA had to alter an rearrangement of Gwen's genes to give Eunice phenotypes that her template lacked, specifically recessive traits like blonde hair and notably contrasting chin shapes. The two things they do share are similar face structures, but most of all their unique green eyes, which the Tennyson cousins share.
- Much of Eunice's origins (namely being a Galvan invention fused with Tennyson DNA) would be carried over to the reboot series in the form of Glitch.