Monster
For the first time in his life, he is unsure of his actions. Before, he has never doubted himself. A criminal needs to be punished. Those that would follow in his footsteps must be shown their folly. So he kills, and kills brutally. He leaves mutilated bodies, but not so that people would not recognize, who the remains belonged to.
It works too. He sees less and less injustice: it has been months since he last caught somebody harassing another person just because they felt like it. The streets are empty after dark: there is nobody skulking in the dark corners, waiting to ambush others.
He has been satisfied with his achievement, until he overheard a mother scold a child. He has no idea what transgression the little boy has committed, but what matters most to him are the mother's words.
"Behave or the Night Haunter will get you!"
The Night Haunter is what the people started calling him. They don't know who he is and believe he is some sort of monster, and that was fine until now. He doesn't mind being a monster as long as he knows he is doing the right thing.
But is he? A mother has just used him to threaten her child. That is not something he had intended. Yes, he wants to be feared, but only by those that would commit a wrong. A child does not fall into this category, does it?
Still, maybe he is not wrong. He does not just want to stop criminals; he wants to stop the injustice from happening. If the children learn that there is a monster that will punish them and that the monster punishes adults alike, they will know not to harm others. They will know that some things are evil and should not be done.
The Night Haunter nods to himself grimly. He doesn't like being feared, nor does he like being a monster, but he does not resent it either. Nostromo needs to change and only a monster can bring that change. So, for others, he will be a monster.