List your favorite character that transitioned from one hero or power to another. It has to be the same person going from one phase to another. It doesn't have to be a name change (example: Black Canary going from the canary cry to more skilled hand-to-hand combat) - just a transition.
Some examples:
Dick Grayson - Robin/Nightwing/Ric(?)
Ayla Ranzz - Lightning Lass/Light Lass/back to Lightning Lass
Roy Harper - Speedy/Arsenal