Chinese zodiac is the 12 animals that make up the 12 different personalities of human beings. The signs always start with the sign of the rat first there are a plethora of stories concerning Chinese zodiac.
According to one legend, the ox would've been the first in the Chinese zodiac had it not been for the rat jumping on his back unsuspectingly and jumping off just as the ox was about to step out of the water. In contrast, it turns out the pig is considered lazy, and therefore took his time and came in last.
You may be wondering why all these animals were swimming across the river? This is because the animals could not decide who should be first in the Chinese zodiac and asked the gods, what to do? The gods decided to have a race across the river to decide who would be first and who would be next based on when they reached the river bank.