Iron Man 2
Stern first appeared in Iron Man 2 where Tony Stark, Rhodes, Pepper Potts, Phil Coulson, and Justin Hammer attend a hearing to try to get Tony to hand over his Iron Man armor due to the potential threat it poses but Stark refuses then turns to Justin Hammer, and eventually was forced to award Stark and Rhodes a medal after he defeated Whiplash, which Stark took much pleasure into.
Stern reappeared briefly in Captain America: The Winter Soldier, where he was seen having lunch with SHIELD agent Jasper Sitwell. After the meeting, as they hugged each other, Stern whispered, "Hail HYDRA." into Sitwell's ears. Secretly, however, both of them were HYDRA agents.
Near the ending, Stern was arrested by various black-suited FBI agents due to his HYDRA membership being exposed due to Fury and Black Widow's leaks.