Which term describes someone that is not capable of being reformed?

The term "incorrigible" precisely describes someone who is deemed incapable of being reformed or corrected. This word is often used in the context of behavior or habits that are so entrenched that attempts to change or rehabilitate the individual are futile. When someone is labeled as incorrigible, it implies a certain permanence in their ways—suggesting that, despite intervention or attempts at reform, they remain unchanged.

In contrast, the other terms do not convey this meaning of irreparability. "Regenerate" refers to the ability to grow or develop anew, indicating potential for change and improvement. "Improvement-seeking" explicitly defines someone who is actively looking for ways to enhance themselves, thus implying a willingness to change. "Malleable" describes something or someone that is easily shaped or influenced, suggesting flexibility and the capacity for change.

In summary, incorrigible captures the essence of being resistant to any form of corrective change, making it the most fitting choice among the options presented.