Regular

In the darkness of the inner city, above the rustle of the never-ending rain, it heard the sound of boots approaching.
A shape appeared in the mist.
It drew nearer.
Water cascaded off a metal helmet and an oiled leather cloak as the figure stopped and, entirely unconcerned, cupped its hand in front of its face and lit a cigar.
Then the match was dropped on the cobbles, where it hissed out, and the figure said: “What are you?”
The entity stirred, like an old fish in a deep pool. It was too tired to flee.
“I am the Summoning Dark.” It was not, in fact, a sound, but had it been, it would have been a hiss. “Who are you?”
“I am the Watchman.”
“They would have killed his family!” The darkness lunged, and met resistance. “Think of the deaths they have caused! Who are you to stop me?”
“He created me.
Quis custodiet ipsos custodes? Who watches the watchmen? Me. I watch him. Always. You will not force him to murder for you.”
“What kind of human creates his own policeman?”
“One who fears the dark.”
“Indeed. But I think you misunderstand. I am not here to keep darkness out. I’m here to keep it in.” There was a clink of metal as the shadowy watchman lifted a dark lantern and opened its little door. Orange light cut through the blackness. “Call me… the Guarding Dark. Imagine how strong I must be.”
The Summoning Dark backed desperately into the alley, but the light followed it, burning it.
“And now,” said the watchman, “get out of town.”

– Quis custodiet ipsos custodes |
Terry Pratchett, Thud!