Thanos
Thanos is a powerful Titan who believes that the universe is overpopulated and must be purged in order to save it. His quest to collect the Infinity Stones to fulfill his purpose leads him into conflict with the MCU heroes.
This character might be one of the most strong-willed villains in the MCU, with immense strength and intellect. In the comics, however, Thanos is in love with Death itself and wants to wipe out half of all life in the universe just to impress it.