Thanos

"Flesh is weak. Weakness must be cast aside for the sake of power."

- Thanos

Thanos, called the Dark Lord by his most loyal underlings, is a powerful alien warlord who rules over a distant region of space and commands a massive army known as the Chitauri. He allied himself with Loki to invade Earth.

Quest for the Infinity Stones
Thanos' past is unknown at this point and how he came to power. Not even his species has been fully discovered. It is known that at some point, he gained control over the deadly army of the Chitauri, eliminated the Zehoberi race and a Luphomoid family and raised the beings known as Gamora and Nebula to be devoted, deadly assassins.

Thanos greatly desired the Infinity Stones, 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.

Through many years of searching, Thanos discovered a lead on the Orb's location, sending Nebula and Gamora to the Cloud Tombs of Praxis under the command of his ally, the Sakaaran soldier Korath. Nebula fell victim to a trap during the mission, and Thanos, not one to tolerate failure, forbade Gamora from rescuing her. Nebula was forced to amputate her own arm in order to escape. The Orb was never recovered, but Thanos let the failure pass and resumed his search.

Aiding Loki
"You will have your war, Asgardian. If you fail, if the Tesseract is kept from us, there will be no realm, no barren moon, no crevice where he can't find you. You think you know pain? He will make you long for something as sweet as pain."

- The Other describing Thanos' wrath

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, he was contacted by Thanos. 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 and the Tesseract transported to Asgard, 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 Earth's heroes would be to court Death. To this, Thanos simply smiled.

The Orb
"Of course, I always was a man with an eye for a bargain. I may be able to help. But there is always a price, is there not?" "What do you want?" "That's easy, Ronan. I want power."

- Thanos and Ronan

Sometime later, Thanos brokered a deal with his old ally, Ronan of the Kree, promising to lend a fraction of his forces in a genocide against the Xandarians in exchange for aiding in the search for the Orb. Ronan discovered the true location of the Orb on the planet Morag and attempted to deliver it to Thanos, but an unexpected turn of events ensued and the stone fell into the possession of human pilot Peter Quill and his allies. Unwilling to be denied another stone, Thanos ordered Ronan to pursue Quill and recover the stone, sending Nebula to aide the Kree in his pursuit.

Powers and Abilities
Thanos' powers are yet unknown at this point. However, it is conceivable that he is extremely powerful, able to strike fear into an Asgardian like Loki and command the Chitauri army unchallenged.

Allies and Subordinates

 * Loki - Ally
 * The Other - Subordinate
 * Chitauri - Subordinates
 * Leviathans - Subordinates
 * Nebula - Daughter
 * Ronan the Accuser - Subordinate
 * Korath the Pursuer - Subordinate
 * The Collector - Enemy turned ally

Enemies

 * Avengers - Enemies
 * Captain America
 * Iron Man
 * Hulk
 * Thor
 * Black Widow
 * Hawkeye
 * Guardians of the Galaxy - Enemies
 * Star-Lord
 * Drax the Destroyer
 * Rocket Raccoon
 * Groot
 * Gamora - Adopted daughter and enemy

Behind the Scenes

 * Thanos' presence in the movie was kept top secret until the release of The Avengers.
 * Damion Poitier was credited as "Man 1" despite actually playing Thanos.
 * Kevin Feige has said that Thanos will likely be played by a different actor in future films.
 * Thanos is the only villain who has interacted, albeit indirectly, with every major hero in the franchise, as he was responsible for the events depicted in The Avengers (which featured all the major heroes of Phase One) and is the mastermind behind Guardians of the Galaxy.
 * According to James Gunn, Thanos is the "head of the snake" in Guardians of the Galaxy and will be motion captured.

Trivia

 * In the comics, Thanos has no relationships with Loki nor the Chitauri, but he's nevertheless one of the Avengers' most historical foes.
 * In the comics, Thanos is the master of the Infinity Gauntlet, which he used in the eponymous series in an attempt to court Death.
 * The name "Thanos" is based on the Classical Greek θάνατος thánatos, meaning "death".
 * Along with Iron Patriot, Howard Stark, Fandral, and the Hulk, Thanos is one of the few characters in the MCU played by different actors in different movies.