MCU: The Worst Thing EVERY Avenger Has Done
11. Winter Soldier - Killing Tony Stark's Parents
The look of shock in Howard Stark's face when he realised that the man about to kill him was his former friend Bucky Barnes - who, by the way, hadn't aged a day - said it all. The look of betrayal on Tony Stark's face as he watched it unfold decades later was even more harrowing. And the look of shock on everyone's faces as they realised what the Winter Soldier had done was probably enough to rival both of those emotions.
That's how much of a shock it was to learn that our beloved kind-hearted Sgt. Barnes from Captain America: The First Avenger had evolved into this monstrosity over the decades that followed. And even though we knew he had killed people before, this one hit that much harder.
It feels wrong mentioning this considering Bucky wasn't in control of his actions at this point in time, but the truth is that Bucky himself never did anything remotely as bad as this throughout the course of his MCU screen-time, making it the obvious choice. The real villains here, however, are HYDRA.