This animal is most like a human, yet we use the word 'ape' to describe how we mimic others. It might be a clue that you are following the crowd and at the expense of expressing who you really are. The ape is also unpredictable and amusing, and can personify the Trickster within you - jarring you from taking yourself so seriously.
When the Ape appears frightening it can symbolize the power of your body that doesn't feel under your control. For example, it is common for a woman going through menopause to experience this power as a frightening Ape. In some ways the Ape will personify your idea of your most uncivilized and wild/natural power - that part of you that is purely instinctual. See also Gorilla and Animals.