4. Red Skull (Captain America: The First Avenger)
Marvel StudiosJohann Schmidt, leader of Nazi Germany's HYDRA division, is played with frightening malice by Hugo Weaving in Captain America's first solo movie. The Red Skull was heavily disfigured as a result of his injection with a prototype Super Soldier Serum, but his mind is undamaged and his body is much stronger than a normal human. The Red Skull gets his hands on the Tesseract, a cube of immense power that is the movies version of the Space Infinity Stone, and begins to conduct tests on it, making HYDRA much more technologically advanced than the Allied army. This leads Captain America and company to pursue the Red Skull, hunting him across Europe and destroying Axis bases as they go. Finally, Captain America gets on board of HYDRA's bomber being sent to the USA and fights with Schmidt; during the fight, Schmidt accidentally touches the Tesseract and is teleported off of the bomber, never to be seen again (will he return at any point?). The Red Skull makes his way to the #4 spot due to his scientific genius, his ruthlessness, his ability to control the HYDRA division effectively, and his physical equality to Captain America, making him a true double threat of physicality and mentality. The reason he doesn't make it higher is his lack of relatability - Schmidt is literally a world-domination-seeking Nazi. Hugo should be proud - a role that he supposedly didn't enjoy playing very much managed to earn the rank of 4th greatest MCU villain.