How do I write a good hero?

I wasn't sure what flair to use. I want my players to eventually meet a badass knight with immense power because he's under direct command to the emperor (a demi god) and I want to make him cool and likeable but I don't know how to introduce him without showing up the party which is something I never want to do and I don't want this to be "the op dmpc that swoops in and saves the day" because I hate hearing stories about that. I want to introduce this character as a powerful ally to have but not a cheat code. TLDR; I want to make an NPC that's powerful and cool but not upstage the party.