The weather trio is a fan term for the legendary trio made up of Groudon, Kyogre, and Rayquaza.
The weather trio could be references to the Biblical mythologies, Leviathan, a sea monster; Behemoth, a land beast; and Ziz, a giant bird, respectively. Also, their role as the guardian, as well as their respective types, are related to the elemental spheres; Kyogre being the hydrosphere, Groudon being the lithosphere, and Rayquaza being the atmosphere.
