Matteus, is the guardian of Raviel, the Lord of Phantasms. The original Matteus was sealed by Raviel, then Raviel created another one under his command. The sealed Matteus is inside the other Matteus and they both are in Hueco Mundo.
The King first created the original Matteus ages ago. Then after some time Raviel used his hypnotic abilities to lure Matteus to his trap and so Raviel sealed him and created a new one.
Because of this, Raviel has the freedom to move from one location to another, but usually prefer to be in one place, and so Matteus became a slave to Raviel.
Abilities and Powers
The original Matteus' powers are still unknown. The newly created Matteus has the same power as the old one, as stated by Raviel, and also has ice, wind and wields a blade, like the old one. Like the old one, the new one is still a celestial being, because the old one is sealed on him.