Nietzsche contributes an analysis of the relationship between power and the self to critical theory. Power is a very important concept - what it is, who has it, where it came from, how it manifests itself, how it disguises itself.
Nietzsche's story goes like this: We are all fundamentally constituted by power, in the sense that we strive to be what we are. We strive to manifestation. There is nothing more. This is why Nietzsche is a nihilist - there is no foundation outside of ourselves that describes who or what we are.
Nietzsche uncovers the ways in which our constitution by power is subverted or co-opted by those who cannot face their own self-creation. A good example is his account of the development of Judaism and Christianity. It happens in historical stages, like this:
1) Yahweh is a God of justice. This is the logic of nations that have power in good conscience. Their festival worship is their affirmation of life. Justice, in this society, follows affirmation.
"in the period of the kingdom, Israel too stood in a correct, that is to say natural relationship to all things. Their Yahweh was the expression of their consciousness of power, of their delight in themselves, their hopes of themselves.
2) After internal anarchy and external oppression have destroyed this natural state, it remains as an ideal-expressed by the prophets.
3) when the ideal fails as an ideal, Yahweh becomes only a God of justice "in the hands of the priestly agitators" who establish that most mendacious mode of interpretation of a supposed "moral world-order". Good becomes a reward, and evil is punishment.
Instead of affirmation establishing justice, justice tries to establish affirmation. God should be a projection of us. We cause God. What God becomes is the cause of us, instead of the effect. We become, as it were, the projection of God, and thereby lose our reality.
4) the priests, who have seized power within Judaism rewrite history in order to disparage the earlier great age in which the priest counted for nothing. The priests are redactors.
Nietzsche's view is that the priests are trying to set up a political system (power), but they call it religious. So, they re-interpret what happened in #1 as being a decadent time that was punished by exile.
5) the rise of Christianity extends priestly ressentiment (resentment, revenge) to all hierarchy and rank by attacking the conception of the Jewish people (chosen people) as such. The Jews are not really chosen. This is the last negation of nobility. It really is a move to even more abstraction. The faith is even further away from the real world, and the two are placed at odds.
What this means is that Nietzsche is showing the entitlements of power as simply being the weak imposing their will on the rest. They don't look weak, but in fact they are. Critical theory is intent on uncovering power relationships like this within society, to show that a putatively "equal" society is really not equal at all, and that its inequality is furthermore invisible to most of those within it.