lokariototal,
What exactly IS the ego?
Without playing semantic games there is more than one answer to this question. It depends on the social and cultural context in which you ask and in which the answer is given. Within western/modern psychology the ego is a lesser thing than in Buddhist thought and psychology. The ego is a nothing, a fiction within the context of Buddhist teachings, thought and experience - yet it is a powerful and much deeper fiction than that ascribed by 'western' thought. Within western traditions it is largely what you describe below:
Correct me if im wrong, but I think of the ego as the mental construct we have of ourselves, and our lives. For example, my name is such and such, I consider myself to be bla bla, I like bla bla, and my past is such and such.
This to me is the ego. It's just a bunch of thoughts that make who we think we are.
As above in 'western' traditions this is true. In Buddhist psychological understanding it runs deeper than this. The ego is this and more: the collection of conscious and unconscious processes of form, feeling, perception, thought and consciousness that make up the sense of 'I, me and mine'.
These are described in the Skandha teachings. And particularly it is important to understand two important aspects:
Firstly the meaning of Skandhda: heap, pile or collection: our existence, experience and conditioning builds these 'heaps' or collections of habitual ways of perceiving, conceiving and thinking about the world. Like a pile of wood, the ones on top are dependent on the ones below. So it is with these aspects of ego: habit piles on top of habit, such that we are barely aware of the root of the 'story of self' you call the ego. There are many unexamined habits underlying that which emerges into consciousness as the story you tell yourself about who you are: herein lies a fundamental difference culturally, Buddhist 'ego' includes a vast amount of subconscious material and processes, and perhaps even genetically coded predilections.
Like a big game of Jenga, it's no use taking a piece off the top and thinking you've 'done it'. You have to let the whole stack fall by pulling out the foundations, the roots: the stories which have accumulated subconsciously to make the conscious story spring to mind/awareness.
Secondly how do you do this? Through mindfulness, awareness, vipassana, introspection: putting yourself under the microscope, dissecting yourself through bare attention.
And in this process, particularly noticing it is not the habits themselves which make up the ego but the habits in conjunction with
attachment to the habits and stories.
This is where what Quardamon writes becomes clear: in different situations we will attach to those pieces in the puzzle/pile which seem most relevant, and thus our ego will manifest differently when we are rowing, chatting with friends, listening to Beethoven or whatever ... The ego constantly reinvents itself from this great pile of possibilities to suit it's environment.
Am I right?
No, but you're not wrong, merely missing some pieces of the puzzle

Warmly,
Matthew