She sacrificed herself for a better future for the entire universe.
He jumped on what seemed to be a live grenade, before he even got his powers.
Groot sacrifices himself to protect the Guardians from a horrific explosion.
In the end, he wanted to be a good father figure to Quill.
Quicksilver riddled himself with bullets to save Hawkeye and a child.
His sacrifice is the sole reason why Ironman became what he is today.