Answer:
kings and queens may cling to power and the jesters may have their call. I am the most common but I can rule them all.
I go in dry and come out wet. The longer I stay in the stronger my surroundings get.
Brown I am and much admired; many horses have I tried; tire a horse and worry a man; tell me this riddle if you can.
Weight in my belly trees on my back nails in my ribs feet I do lack.
I go inside boots and outside shoes.
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.