In Hindu philosophy, ignorance of the True Self causes ego and the perceived distinction between consciousness and physical matter, between mind and body. In Eastern religions, the human being is often conceived as being in the illusion of individual existence, hence considers himself as separate from the macrocosm, the Universe. The state of illusion, or Maya, gives rise to egoism and desire. For a person seeking enlightenment, the main goal is to bridge this polarity, to dissolve the ego, and see that the Self and the Universe are one.
Lao Tzu, in his Tao Te Ching, says "Knowing others is wisdom. Knowing the self is enlightenment. Mastering others requires force. Mastering the self requires strength."
The German/ Canadian spiritual teacher, motivational speaker, Eckhart Tolle, has written at length about the ego in his book A New Earth.