Thanos

Thanos, referred to as the Dark Lord by his most loyal underlings and the Mad Titan by the galactic community, is a powerful, cosmic warlord who rules over a distant region of space and also commands two massive armies known as the Chitauri and the Outsiders. His own main objective is to obtain the Infinity Stones, and his desire to achieve this goal is what led him to forging deals with Loki and Ronan the Accuser in their respective campaigns against Earth and Xandar, promising to aid them in exchange for an Infinity Stone. Both of these new alliances cost Thanos much of his resources, including one of the stones and the loyalty of his two daughters, Gamora and Nebula, and inadvertently resulted in the formation of the two superhero groups: the Avengers and the Guardians of the Galaxy. Fed up with these failures of his servants and opted to seek out the Infinity Stones himself.

Will be continued in Infinity Wars