BloodClan are a large and formidable group of feral cats led by the ruthless Scourge and villains in Erin Hunter's Warriors book series, appearing as the main antagonists in the original "The Prophecy Begins" series, The Darkest Hour.
BloodClan is a loosely organized group of hostile alley cats who live together in Twolegplace (a human town) for mutual protection from Twolegs (humans). They mostly feed on trash. Live prey is scarce, except for the occasional rat.
Their founder and leader is Scourge (formerly named Tiny), a small black cat with one white paw, icy blue eyes, and an eerie, high-pitched voice that sounds like the splintering of ice. They don't have an "official" deputy, but the cat closest to Scourge is a muscular black and white tom with green eyes named Bone. He does most of Scourge's dirty work, and keeps the other cats of BloodClan in line by force. The highest ranked cats in BloodClan attach dog teeth to their claws to look threatening to other cats and to make their blows more effective while fighting. They do not have a medicine cat, and the elders, queens, and kits are never cared for; if a cat can't hunt for itself, then that cat will die.
Cats are required to live on their own, and living in family groups is forbidden, given Scourge's concern that some cats will join together against him. Mothers are forced to train their kits, teaching them how to hunt, fight, and generally everything basic, and at the age of twelve moons, kits leave their mothers, so they are forced to rely on Scourge and Bone.
It is revealed that BloodClan's biggest weakness is their disbelief in StarClan, the spirit cats who guide the living cats. This means that the leader will not receive nine lives, which is proven when Scourge is killed by Firestar.
BloodClan was founded by Scourge, a runty black tomcat, who rallied and encouraged other ally cats, who eventually copied his ways.
Tigerstar, the ambitious leader of TigerClan, forms an alliance with BloodClan at the beginning of The Darkest Hour, in the hopes of using the combined might of TigerClan and BloodClan to convince any resistant Clans (namely LionClan, comprised of ThunderClan and WindClan) to join TigerClan. In exchange, Tigerstar agrees to give BloodClan a share of the forest to live in, after all the Clans join TigerClan (although Tigerstar has no intention of following through on that part of the bargain). However, the plan backfires when Tigerstar finds that he cannot control BloodClan, and is killed by Scourge, in one terrible blow that destroys all nine of Tigerstar's lives at once.
Scourge, who by then had decided to take the territory for himself, gives the Clans three days to leave. Firestar manages to convince the four Clans to form LionClan to take on BloodClan. During the three days, several cats, particularly Jaggedtooth and Darkstripe, turn traitor to their Clans and join BloodClan. At the end of the three days, LionClan and BloodClan meet in battle. The death toll is heavy, the most prominent being Whitestorm of ThunderClan. Scourge takes one of Firestar's nine lives before Firestar is able to kill him, ending the battle. Without a leader, BloodClan scatters and retreats back to their old home in shame.