Sri Ramana Maharshi - Spiritual Instruction, Ch. I, § 12

The individual being which identifies its existence with that of the life in the physical body as ‘I’ is called the ego. The Self, which is pure Consciousness, has no ego-sense about it. Neither can the physical body, which is inert in itself, have this ego-sense. Between the two – that is, between the Self or pure Consciousness and the inert physical body – there arises mysteriously the ego-sense or ‘I’ notion, the hybrid which is neither of them, and this flourishes as an individual being. This ego or individual being is at the root of all that is futile and undesirable in life. Therefore it is to be destroyed by any possible means; then That which ever IS alone remains resplendent. This is Liberation or Enlightenment or Self-Realisation.