The T-elos project was headed by a man named Roth Mantel, an alias of, a mysterious Vector scientist. As Roth Mantel means "red cloak" in German, and with Kevin Winnicot revealed as the Red Testament, it seems he is her designer, especially with her resemblance to KOS-MOS.
In the course of the Xenosaga events, it is revealed that KOS-MOS was a step in the development of T-elos intended to serve as the vessel for the resurrection of Mary Magdelene "the partner of the Messiah". T-elos herself was created from the bodily remains of Mary, and thus may be considered more of a cyborg than an automaton. In order to complete the process for the resurrection, T-elos intended to destroy KOS-MOS which had become the vessel for Mary's spirit.
In their first engagement, T-elos demonstrates that she is clearly more powerful than KOS-MOS. In the ensuing fight KOS-MOS states that T-elos output is 4.75 times her own. In the ensuing fight, KOS-MOS only manages to connect with a single attack against T-elos. Meanwhile T-elos lands a number of staggering blows against KOS-MOS. It is clear from the start of the fight that T-elos clearly outclasses KOS-MOS. While KOS-MOS is able to outlast her own estimate against T-elos, she is defeated when struck by T-elos' Phase Transfer Cannon. T-elos then uses her heel to crush KOS-MOS' chest, disabling her. The damage inflicted in the fight was such that KOS-MOS had to be completely rebuilt in order to function again.
In their second encounter, T-elos squares off with a rebuilt KOS-MOS. T-elos proves able to easily overwhelm the other party members, but is eventually defeated by KOS-MOS following an exchange of Ether, via Phase Transfer Cannons. As T-elos lay defeated, she is embraced by KOS-MOS as the two resonate with one another. T-elos disseminates becoming one with KOS-MOS, thus allowing Mary to finally be resurrected in both body and spirit.
Project X Zone
T-Elos makes an appearance in Project X Zone. She is a boss and a playable character who is partnered up with KOS-MOS.
The latest model battle android developed under the anti-Gnosis Project Zohar. "Telos" means "ultimate state" or "unlimited power" in ancient Greek, a fitting name since she once displayed power far above that of KOS-MOS in a previous battle between them. Also, unlike KOS-MOS, she is capable of displaying emotions. She is high-handed and has a cruel side that simply enjoys causing destruction. Fixated on obtaining something that KOS-MOS possesses, she attacks her relentlessly, once even almost totally destroying her. Just as with KOS-MOS, T-elos's body conceals a secret.