Ivan Vorpatril in the Bujold's Vorkosigan saga. He is a very different character to the hyperactive Miles and being his cousin has known him forever. So he both moves the story on and shortens the storytelling - as in he's able to say "oh, not that again, he hasn't done that in five years" or "he's in one of his funks" and then briskly moves the story on by dropping Miles in a bath of ice water to get him out of the funk.
He's now got his own book (which I'm waiting to come out in paperback, so no spoilers please).
He's now got his own book (which I'm waiting to come out in paperback, so no spoilers please).