Mule
Since the mule is the offspring of two different species but is itself infertile, it can be seen as a symbol of the premature union of opposites.
The mule is an excellent pack animal—reliable, strong, resilient, very stubborn, and capable of navigating almost any terrain.
From a symbolic perspective, however, it has carried a negative connotation due to its infertility. That which is unfruitful cannot bear fruit, according to symbolic thinking. In the past, a person considered bad or unproductive might be called a "mule," implying someone from whom no good could come. (See also Donkey.)