"A scourge on the name of all good cats!"

Scourge is a character from the Warrior Cats book series. His initial appearance is in 2004 in The Darkest Hour, the 6th book of The Prophecies Begin. Later, in 2008, he got his own standalone manga, The Rise of Scourge, detailing his backstory. He has a cameo in Bluestar's Prophecy, which was released in 2009.
Scourge is a small black cat with one white paw, nicked ears, and blue eyes. He wears a collar of contentious color (usually red or purple) that is embedded with dog teeth. His claws are also lengthened by dog teeth.
Scourge has long been a fan-favourite character. He is most well known for a scene in The Darkest Hour where he disembowels Tigerstar, the main antagonist up to this point, instantly killing him ninefold.

Scourge was originally born as a kittypet named Tiny. He was the son of Quince, and the brother of Ruby and Socks. Tiny, being the runt of his litter, was frequently bullied by his siblings, who told him that if he wasn't chosen by a twoleg, he'd be sacked and thrown down a river, left to rot in the murk and silt.
Afraid to die and determined to prove himself, Tiny ventured off into the forest where the fearsome Warriors lived. Tiny was caught by Tigerpaw, who near-fatally brutalized him.
Tiny could not go back to his home, and he ventured off into the slums of twolegplace. In an attempt to remove his collar, Tiny got a fallen dog tooth stuck in it. This ended up working in his favor as, starving, he lied to fellow street cats that he had killed a terrible cur and taken the tooth as his trophy.
All was not well though, as he soon had to put in bite and not just bark. Having heard his story, Bone and Brick approached him to request his help in warding off a dog. Through a stroke of luck, Tiny managed to scare off the dog using his shadow. He was no longer Tiny—but Scourge.
Cats soon flocked to Scourge for advice and protection. He gained a reputation as the most feared cat in all of twolegplace; a cold-blooded killer. But despite having the entire city under his paw, Scourge was not happy, as he had not the thing he wanted most: revenge.
Scourge continued to bide his time until Tigerpaw, now Tigerstar and having long forgotten their altercation, sought him out for help. Scourge betrayed Tigerstar at the last moment, gutting him before an entire Gathering of cats. At long last, Scourge was fulfilled. Standing strong under a deluge of blood, Scourge had proven that he was strong.

Scourge is my favorite character in all of Warrior Cats, and honestly, my favorite character of all time. Rise of Scourge shows him as a surprisingly reasonable cat, it even being cited a major reason why he rose to power. He isn't needlessly violent, and while he rules by fear, he relies more on intimidation than actual bloodshed. He's cunning and tricky. He's even quite kind, willing to put aside his biases against them when Ruby and Socks need help. Overall, Scourge is strong and determined—he doesn't allow his personal feelings to get in the way of what must be done.