Besides Clark Gregg playing Agent Coulson, there have been several other agents added to the cast. However, it looks like these other agents will be playing a background role to Agent Coulson.
Cobie Smulders said, “Joss Whedon is a genius, and any opportunity that I have to say words that he has written I will take. And Clark, this is sort of his show, Clark Gregg. And I love Clark and want to sort of be a part of it, but we’ll see.”