I would say Light Yagami from death note.

After finding the notebook that kills the person whose name written on it, he then follows his wicked sense of justice with the ultimate goal of cleansing the world with evil doers - killing the world’s dangerous criminal.

Although he had all the good intentions, Light became corrupted with too much power where he started using the book for his own personal gains. But in the end, the worldwide crime rate was down to 70% thanks to his work.