Thrushstone

Thrushstone is a cat you don't want to take lightly, as he's been known to lose his temper. 

He was once a ThunderClan warrior, but was exiled for killing one of his Clanmates by breaking her leg and throwing her in front of an incoming car. He tried to get his son, Pinepaw, to come along with him, but the apprentice refused, as the cat his father killed was one of his friends. 

Out of spite and anger that his own son had turned on him, Thrushstone left ThunderClan, ordered to be killed on sight if he was ever caught on their territory again. 7 moons after his exile, a patrol had found him, but he was already dead - a large group of rats had killed him, and as he was outnumbered, Thrushstone was unable to power through them.

For his actions, he was sent to the Dark Forest, chosen to be the second-in-command by Houndstorm.