The Order of the Guardians existed for many years, inhabiting a temple where the inactive Miraculouses were kept. However, when Wang Fu was young, he made an unspecified mistake that resulted in the temple being destroyed, the Moth Miraculous, Peacock Miraculous, and Miraculous spellbook being lost as well. Wang took the remaining Miraculouses in the box, and he has kept watch over them by himself since then.
Guardians are chosen as children to be trained for many years in order to be prepared for the task of watching over the Miraculouses. They are taught to understand the code in the Miraculous book, although Wang wasn't able to learn it completely before the book was lost.