Thanos (Marvel Cinematic Universe)

 "The only matter I do not take seriously, boy, is you. Your politics bore me, your demeanor is that of a pouty child. And apparently, you have alienated my favorite daughter, Gamora. I shall honor our agreement, Kree, if you bring me the Orb. But return to me again empty-handed, and I will bathe the starways in your blood."

- Thanos to Ronan the Accuser

  Thanos is a powerful alien warlord who rules over a dead dimension and commands a massive army known as the Chitauri. He allied himself with Loki to invade Earth, and allied with Ronan the Accuser to destroy Xandar, both in exchange for the deliverance of two powerful infinity gems, but they both failed to accomplish this task and had betrayed him.

Thanos is the true main villain in The Avengers and one of the major antagonists of Guardians of the Galaxy. He will (presumably) be one of the main adversaries of Avengers: Age of Ultron and will be the mostresumable antagonist of Avengers: Infinity War - Part 1 & Part 2.

He was portrayed by Damion Poitier in The Avengers.

He is portrayed by Josh Brolin in Guardians of the Galaxy and for future installments where they show his character.

History
Thanos' past is unknown at this point and how he came to power. Not even his species has been fully discovered, sans the assumption that he is an Eternal. It is known that at some point, he gained control over the deadly army of the Chitauri, and took the assassin Gamora as his daughter. Thanos greatly desired the Infinity Gems, objects of immense power that held considerable dominance over the various forces that occupied the universe, and forged several alliances in order to locate them.

The Avengers
At some point during his quest, Thanos discovered that the Tesseract, the Space Stone, was on Earth, and allied himself with the exiled Loki providing him with the Chitauri, who would help him conquer the planet in exchange for the Tesseract. Once Loki had arrived on Earth, he succeeded in acquiring the Tesseract, but as he was preparing for his invasion, Thanos contacted him. Through his intermediary, The Other, Thanos threatened the Asgardian god of mischief, saying that if he failed in delivering the Tesseract, Thanos would force him to endure a new kind of suffering.

After Loki was defeated, the Other reported to his master that the Earth's inhabitants were not as weak as they were thought to be. He also declared that challenging the heroes would be to court Death. To this, Thanos simply smiled...

Guardians of the Galaxy
Thanos destroyed Gamora's planet and her kind, but took her under his care as an adoptive daughter and trained her as an assassin along with Nebula. Ronan the Accuser made a deal with Thanos - to retrieve a mysterious artifact, and in exchange Xandar will finally be eradicated. However Ronan breaks the deal, thinking that with the Infinity Stone he no longer needs Thanos' help to wipe Xandar out. Both Gamora and Nebula wanted to be free from Thanos, the former betrayed him by joining Star Lord and the latter swore allegiance to Ronan and promised that she'll destroy 1000 worlds for Ronan for freeing her from Thanos.

Agents

 * The Other - Second in Command - Deceased
 * Loki - Formerly - Alive
 * Ronan the Accuser - Formerly - Deceased
 * Nebula - Formerly - Alive
 * Gamora - Formerly - Alive
 * Chitauri-Army - Deceased