Glaive Le Gable is the Guardian of Mud but is also the source of life for all of Filgaia, including the other Guardians, the Elw, and the Humans. Despite the tremendous sort of power that creation at this level must entail, Glaive Le Gable is not sentient; it merely goes about its process of regulating the life-force of Filgaia. Glaive Le Gable is humongous in size and is essentially the core of the planet. Glaive Le Gable only appears in Wild Arms 2, as the final dungeon of that game.
It is possible that Glaive Le Gable exists in other incarnations of Filgaia as depicted in other Wild Arms titles; if you speak with Armengard in Wild Arms 3 on October 29th, she will say this: "Today is October 29, Toy Day. Collect all 12 Saint Guardian action figures and get a free Guardian of Mud [Grablugable] doll! I wish I'd known that before the offer expired... Sigh."