Do yourself a favor and listen to this.

"Dynamic Duos: The Famous Partnerships in Advertising" from Terry O'Reilly's Age of Persuasion, listen it here. It's a half hour look through the relationship between a client and an agency creative and what it took for those two to create some of the best ads of all time.  Phil Knight (Nike) and Wieden, Jobs and Lee Clow, Gallo and Hal Riney.  Really interesting listen.