Darkcedar

Darkcedar is a tom who had a very bad upbringing. He is the unwanted product of a cross-clan relationship, and after his mother's death during kitting, he was raised without love by a queen who had lost her own kits. She had wanted desperately to reject Darkkit, but his father, Tigershade had threatened her life so that he would live. But even he didn't love his son. He only kept him alive so that his mother, who he thought was worth nothing more than dirt, wouldn't be able to protect him in Starclan. Tigershade had never been a cruel tom until he began facing prejudice for his Thunderclan lover, and eventually turned that on her. Cats he grew up with became afraid of him, and his sadistic tendencies. They were afraid he would do something to harm them, and he threatened them when they tried to speak out. Very young, Darkkit learned that he could gain his father's approval by fighting and would constantly push to gain it. Tigershade knew what he was doing, he kept drip-feeding his son love and affection to warp him into the kind of rage-filled, evil cat he wanted him to become, so that his former mate could never see him in Starclan. Darkcedar began to think that it was the right way to live. After his warrior ceremony, he was appointed an apprentice, a young, flighty she-cat called Doepaw. She was terrified of him. Darkcedar, by this point, had shelved any emotions other than hatred, and the desire to become powerful. He overworked the apprentice- who was underdeveloped for her age, barely bigger than a kit. His father praised him on training her to be so strong, and Darkcedar only overworked her more. Eventually, Doepaw collapsed during training, and instead of helping her, Darkcedar was overcome with rage, and he pinned his apprentice to the ground, ending up killing her. Afterward, he felt guilt bubbling up inside of him, but when he saw his father watching, and his nod of approval, he swelled with pride. It was meant to happen.

Darkcedar was never truly identified as her killer, but there were definitely cats suspicious of him. Maybe eventually he could be redeemed, but it will take a long time of undoing the damage his father did to him.