Am I building my own career, or just his?

You work close to someone powerful. His decisions move the room. Yours mostly serve his. This is not shameful — it is simply the shape of the job you took. The question is not whether you are in his shadow. You are. The question is what you are doing with the light that reaches you there. Most people in this position flatter themselves in one of two directions. Either they tell themselves 'I am really the one who makes it work' — a private grievance that changes nothing. Or they tell themselves 'my time will come later' — a promise no one made them. Both are ways of not looking directly at today. You do not control whether he shares credit, whether the org chart moves, whether history remembers your name beside his. You control what you build in yourself while you are here: which judgments you are trusted to make alone, which relationships are yours and not his, which skills you could take out the door tomorrow and sell. Examine that. Nothing else is yours to examine.