Senator Stern is a Congressional senator in Captain America: The Winter Soldier.
Iron Man 2
He first appeared in Iron Man 2 where he repeatedly tried to get Tony Stark to hand over his Iron Man armor, and eventually gave him a medal after he defeated Whiplash, also "pricking" him as a subtle insult to him.
He reappeared briefly in Captain America: The Winter Soldier, where he was interacting with SHIELD agent Jasper Sitwell. Secretly, however, both of them were HYDRA agents. He later appeared again near the ending, where he ended up arrested by various black suited agents, presumably due to his HYDRA membership being exposed thanks to Fury and Black Widow's leaks.