Legend has it that one day Buddha asked all the animals of creation to come to him and promised them a reward if they would come. He must not have been under any illusions, because only twelve animals accepted this invitation.
The rat appeared first, followed successively by the buffalo, the tiger, the cat, the dragon, the snake, the horse, the goat, the monkey, the rooster, the dog and finally the good old pig. Buddha gave each animal a year and named it after him. So the rat received the first year, the buffalo the second, etc. ? and finally the pig the twelfth. All agreed to this.
Thus, since then, each year is marked by the characteristics of one of the twelve animals. Not only the people born in that year, but the whole year itself with all its events are under the influence of the ruling animal.