"This little girl, who's not even half my size… taught me that tears can flow even from these silver eyes."
Before her death at the hands and sword of a novice warrior assigned to her execution party, Teresa was best known for her skill in effortlessly killing enemies with a faint smile. As the strongest warrior of her generation, she was considered to be the most powerful Claymore of all time. While little is known about her life before becoming a Claymore, she is able to make a guess that her parents named her Teresa after one of the Twin Goddesses of Love out of their love for her and that she remembers having black hair that she had believed to be her best feature.
At some point she is given away to the Organization, whether this is done by her village or family is unknown nor ever clarified. It is however known that all orphan girls Like all of the other girls that ended up with the Organization, she too was implanted with the flesh and blood of a yoma, which is a monster that varies in its shape and even feeds on human flesh. After the yoma flesh and blood is implanted, it leaves it's mark in the form of a stigmata on their abdomen. As a trainee, she would escape from the handlers, giving her the name of "problem child" as she would often disappear at the first opportunity when the trainer's attention was completely elsewhere. During one of her escapes, she met the exiled warrior, Rafaela, who was amazed that she as a trainee could survive on her own in a wilderness infested with yoma.
Once she became a full warrior, Teresa could no longer turn back to join the humans in their own world and her life fully belonged to the Organization - a shadow group that creates half human-half monster hybrids to be warriors and send commands for them to go after yoma and Awakened Beings. From that point on she became one of the best known Claymores that Organization had employed among their 42 warriors. It is likely that she realized that there was no place for her among the humans. She is 77th generation Claymore wielding hybrid as warrior 182 of her kind. As solitary as the warriors were, it may have been that she was at least known acquaintances with other Claymore wielding hybrid that went by the name of Irene, Sophia, and Noel though she was much closer to Irene.
But after meeting Clare for the first time after the assigned hunt of a yoma group and starts to spend time with her, Teresa changes emotionally in regards to the human girl. In the beginning of their traveling together however, she did not accept the girl's company and even loathed her in the beginning. She opens up emotionally to Clare and begins to act maternal from that point on. This is something that in Irene's opinion that eventually led to Teresa's own eventual death.
Teresa's execution was swiftly ordered after she had lost control of her emotions and had killed a group of humans bandits that had attacked and destroyed a town where Teresa had left Clare at after getting the yoma that had been terrorizing the town before she had been given her assignment to go there.
While her exact age however is not given by series canon, however a personal guess and through a small discussion with some other fans regarding the age of the characters would be that she likely would be around or would be 30 years of age by human count.
Outwardly, Teresa was a harsh cold-blooded and a solitary killer before she had met the human child, Clare. She did as ordered by the Organization without complaint against the orders that were given to her by her darkly cloaked handler, Orsay.
However as a human child, she was likely much more different, possibly even more adventurous as a trainee than when she was as a Claymore. For example where she may have disliked a certain temperature as a human, it wouldn't bother her as much since she became a hybrid warrior.
There is a small part of her however like other Claymore, that misses being a human and having a human life when she had been a human child. Though however she does hold contempt towards the humans as they are weaker than themselves, and needing their protection from the yoma.
Teresa does have a violent side as most of the hybrids would, which wouldn't make her at all afraid to let others know what she is. She does however take time to enjoy in the bloodshed of yoma that she was assigned to hunted and subtly threatening the humans that she would meet on her assignments.
Sometimes she will have a faint smile on her face, both in and outside of her hunting assignments, its something of a habit.
Teresa's personality is still much the same as it was in her world before her death. But she is slowly starting to open up to the ones that she allows close to her.
Like all Claymores that are employed by the Organization, Teresa is also much stronger than a normal human is. In Canon Teresa's powers, or rather her Claymore abilities made her one of the most powerful warriors of her generation. More powerful than even the former Number 1 that had held the ranking previous to Teresa becoming a warrior and rising through the Claymore rankings.
Her strongest power is that she has the rare skill of unparalleled yoki sensing that none of her fellow warriors have. As a Claymore, she also has the ability to sense the yoki of her fellow warriors and the Yoma that she was assigned to hunt down. And while she is an offensive type warrior she was not focused on protecting herself, she was able regenerate after any damage that was done to her. She could even reattach any severed limbs that may have been lost in battle.
She is also much faster, stronger, and even much more agile that of the 42 warriors that are ranked below her rank of Number 1 in the Organization. Teresa is also able to strike down her hunted opponents before they can even register what is going on at the time when they happen to first see her.
Unlike other Claymore who often use more than ten percent of their power on jobs against their targets. Teresa is able to use only a mere ten percent to take down her opponents including the former Number 1.
While their Claymore swords don't have any powers of their own, they are however sturdy and strong enough to pierce through yoma and Awakened Being hides to take off their heads.
Clare - She develops a sort of mother-daughter relationship with the little girl, despite having been previously annoyed with Clare's persistence to follow her everywhere.
Irene - She shows some familiarity towards Teresa. So they might have had something of a friendship before she was assigned to the Teresa's execution party.
Orsay - One of the men in black clothes in her world, who was assigned to be her handler when she had become a warrior.
A bit of a work in progress