The ego does not exist. It is nothing but a mere idea!
The ego is unreal or illusory, whereas the concepts that the ego is a thought or an idea and does not exist are false. However, the ego is unreal, to the same extent that the body, thoughts, emotions, all animals, plants and in general everything in the universe, as well as the universe itself, are unreal.
As the word or thought 'sea' is an idea but not the sea itself, so the word 'ego' is an idea but not the ego itself. The ego exists just as the sea, the earth, the mountains and also more subtle things like electromagnetic fields, thoughts and emotions exist.
The entire universe and everything that exists in it (including everything invisible to the senses and, of course, the ego) is constructed by the three gunas (sattva, rajas and tamas), which are the fumdemtal powers that create everything. The human being and everything that constitutes the human being (body, mind, intellect and ego) is created by the three gunas. So if we accept that the ego does not exist, then we would have to accept that all beings, planets, stars, animals, plants and the whole universe do not exist.
The ego is psychic energy and, therefore, is not perceptible by the five senses, but we can perceive it (feel, be aware of it) directly through self-observation, just as we can perceive (feel, be aware of) anger, envy, gluttony, etc.
The essential nature of the ego is desiring and creating the feeling of identity by identifying with the body. That is, the feeling "the body is me" is generated by the ego. The ego is also the factor that creates all kinds of identifications. It makes us identify ourselves, with the characteristics and functions of the body, the mind and the intellect (thoughts, imaginations, fantasies, ideas, concepts, beliefs, emotions, feelings, etc.), with objects, people, situations, organizations, religions, political parties, sports teams, dogmas, etc.
It is true that there is no effect without cause. Just as there is no light or heat without the sun, so there is no desire, identification, attachment, pride, anger, rage, fear, greed, jealousy, etc. without ego. Therefore, if there were no ego, there would be neither identifications nor egoistic tendencies.
The tendencies that we call defects are all forms of expression of the ego. The ego is that which expresses itself as anger, lust, lasciviousness, liking, disliking, greed, pride, and so on. There cannot be pride, for example, without ego, and conversely, ego without pride, because they are the same thing. Just as water under certain conditions assumes the form of ice, clouds, steam, hail or snow, so the ego according to the circumstances expresses itself as pride, desire, lasciviousness, jealousy, anger, fear, etc. Ego and egoistic tendencies or defects are the same thing. Therefore, if we accept, for example, that anger exists, we cannot deny the existence of the ego.
That is why in Greek mythology they symbolize the plural nature of the ego as a monster (called the Hydra of Lerna) that had many heads. Each head is one of the tendencies or defects of the ego.
