Metaphysically speaking, the ego is a linguistically manifested identity utilised as a reference point to consciously comprehend the external. This is what 'I' think, what 'I' see, what 'I' believe - this is who 'I' am. Ego is routing consciousness through thoughts; that means every thought you have is ego; it's all ego. Ego holds no real substance, which means what you think to be true doesn't either, which means your identity doesn't, or reality, thus the illusion. A witty person will consider the contradiction that based on this understanding, this is a thought, and therefore lacks validity, proving it incorrect. However, it's proven valid in its undoing, for both ego and this understanding cease once you stop all thoughts. That is the state of meditation.
If your ego does not know itself to be illusory, you're bound to be played by others, particularly your culture. You will go about life filtering this experience through such a shallow pool of understanding. For example, consider how you and your world are a matter of your lexicon, for as you look around, you will refer all that you see to an internal dictionary - a dictionary given to you by culture. Consequently, what's before you isn't what's really there, as what's perceived is first referenced to your language, then culture, then ideology, and so forth until the external thing you see is entirely altered into something else. Tragically, most people perceive themselves in words, not truth, so they never realise how phenomenal they naturally are.
Look, what is the situation if you took a fourteenth-century orthodox Middle Eastern man and a sixteenth-century orthodox Irishman and located them in the same room? You'd have two humans sharing the same space, comprised of the same source, yet living dimensions apart. However, if you found them as they were born, time-travelled to the present, and raised them under your house, in your country, in your culture, with your religion, your language - their reality would hardly differ from one another until perhaps they became adults. That is the connection between ego, language - reality.
"So if I'm not me, these thoughts, who am I?" Well, ironically, let's think about that. Right now, you're flowing, occurring, along with everything. Your being is a continuation of the grand cosmic giggle. Your heart is beating, blood circulating, nerves tingling, cells duplicating, atoms combining, planets forming, stars dying, universe expanding - you are this happening which your ego has no involvement in because it doesn't exist in the first place. If you don't believe me, don't think, feel; feel down into your core in solitude until you're so far within that your thoughts are unheard, and you unearth a self that is much more us than I.