Superman has a pet monkey named Beppo.
Beppo was originally a test animal used by Superman's father Jor-El to develop a spaceship. The monkey stowed away on board of the craft when it launched baby Kal-El to earth.
Because it's from Krypton, Beppo the monkey had super powers ... that it used for mischief! Superboy had to lead the super monkey into deep space and left him there.