To quote Eckhart Tolle, Ego is the Primitive Fight or Flight mechanism we have had since we were in a far more primitive state and in dangerous surroundings. It is the self that needs to resist, exclude and oppose.
It is like taking a me versus them stance, if you get into an argument or fight your ego takes over.
It is also what causes people to try and look like the model on the front of a magazine or wearing the most expensive clothes, driving the best
Movie Stars, Rock Stars, Sporting Stars, Politicians, CEO's of big corporations all have big ego's, thats what helped them get to the top.
In a spiritual sense it is pretty outdated, try listening to your higher self as your innervoice, humility and lack of self- certredness may not get
you a hit record but it will help you in a spiritual sense.