Darth Vader Betrays The Emperor

This scene is in Return of the Jedi. Darth Vader betrays the Emperor and kills him to save Luke.

The Duke of Zill Betrays Zygon
The Duke of Zill betrays Zygon and kills him to save Kristoff.

Ratigan Betrays Baron Greenback
Ratigan Betrays Baron Greenback and Kills Him to Save Bernard.