Thanos, referred to as the Dark Lord by his most loyal underlings and the Mad Titan by the galactic community, is a powerful Titan warlord who rules over a distant region of space and commands two massive armies, known as the Chitauri and the Outriders, and a small group of followers known as the Black Order.
His own main objective was to bring stability from the universe, as he believed its massive population would inevitably use up the universe's entire resources and condemn it. However, his methodology to succeed was warped; through using the Infinity Stones, Thanos intended to harness their power to exterminate half of life in the universe.
Real Name: Thanos
Portrayed by: Josh Brolin
1. Avengers: Infinity War
He spent many years hunting down infinity stones. His desire to achieve his ultimate goal led Thanos to forge new alliances with Loki and Ronan the Accuser in their respective campaigns against the Earth and the Xandar, as seen in his promising to aid them in exchange for an Infinity Stone.
Both of the new alliances had cost Thanos much of his resources, including one of the stones and the loyalty of his daughters, Gamora and Nebula, and inadvertently resulted in the formation of the Avengers and the Guardians of the Galaxy.
Fed up with all the failures of his subordinates, Thanos had opted to seek out the location of the Infinity Stones himself. Thanos engaged in a ferocious warpath in order to obtain all of the Infinity Stones.
In his journey, both he and his Black Order invaded Xandar, Earth, and Knowhere and even murdered Loki, along with half of the surviving Asgardians, and even his beloved Gamora.
The primary aggressors against Thanos became an alliance which comprised the Avengers, Masters of the Mystic Arts, Guardians of the Galaxy, and the nation of Wakanda. Despite facing off against a powerfully combined opposition and the wrath of Thor, Thanos had ultimately triumphed over his enemies once he completed the Infinity Gauntlet, using this to finally complete his goal and destroy half of the life within the universe at the snap of his fingers.
2. Avengers: Endgame
Following his Snap, Thanos had then ensured this could never be reversed by destroying all of the Infinity Stones, resulting in the Avengers tracking him down on Garden before then being decapitated by Thor. However, in the alternative 2014, Thanos was alerted to the events of the Infinity War by a time-traveled Nebula, resulting in him traveling to 2023 and laying siege on the Avengers, as he had just decided to instead wipe out the entire universe and replace it out of revenge for their efforts to stop him.
However, Thanos had been just too late to stop the Snap from being reversed as thousands of heroes returned to stop him. Despite all of Thanos' best efforts, he was unable to claim victory as Tony Stark used his armor to utilize the Infinity Stones, and had decimated the Chitauri and Outriders, as well as Thanos himself, finally ending his reign once and for all.