Teresa of the Faint Smile (微笑のテレサ, bishō no Teresa, lit. Smiling Teresa), known for effortlessly slaying enemies with a faint smile on her face, is the strongest of her generation and considered to be the most powerful Claymore of all time. She is much faster, stronger, and more agile than those below her, but her real strength is considered to be her "unparalleled ability to sense Yoma aura." She can sense it to the point where she can accurately predict her opponent's moves in battle. Despite facing an awakened former number one, Rosemary, she has never used more than ten percent of her full power, which is only enough to change her eye color. Before becoming a Claymore, she was referred to as a "problem child" by her handlers during her training.

Teresa initially does her job without caring about who she is helping, and she takes pleasure in scaring humans. She eventually meets Clare, who decides to start following Teresa after being abandoned by her village. Teresa is initially irritated, but soon grows fond of her.

(Source: Wikipedia)