Mukashi no Enma Zanpakuto ( Ancient God Zanpakuto ) is what shinigami calls the three ancient, powerful and ownerless zanpakuto. Although, this zanpakuto has no name, this is what most calls it.
This three blades were once one and owned by an ultra-powerful being. It's owner became invincible and he never lost a single battle.
Over billions of years, its owner became power-hungry and he soon desired to take the whole spiritual world, but failed, he couldn't accept defeat, therefore he killed himself using his blade.
The King decided to destroy the zanpakuto, but failed, only dividing it into three blades which is also powerful but has limited power, unlike the original one. The three blades were soon placed into different places. One, is in Soul Society, the other is is the Human World, and the last, is in Hueco Mundo.
Legends say that the three blades, once united will form the ultimate weapon, but finding it will be most difficult, it is said that they are guarded by ancient spirits to prevent every creature from getting it.
Over the time, these creatures gained a different form. Some say that they became more active and their guardians are having a harder time guarding them, except Matteus, who was already defeated by Raviel and sealed.