Thanos

"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 alienated my favourite 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, known as the Dark Lord by his most loyal underlings and dubbed as the Mad Titan by the galactic communities, is a powerful cosmic 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 and with Ronan the Accuser to destroy Xandar. His main objective is to obtain the Infinity Stones.

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

- Thanos

Thanos become one of the most powerful and feared warlords ruling over a distanct region of space, having gained control over the deadly army of the Chitauri, eliminated the Zehoberi race and a Luphomoid family to raise two young women from both races, Gamora and Nebula, to be devoted and 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. He successfully located at least one of the stones, a blue gem that was capable of manipulating minds.

Through many years of searching, Thanos discovered a lead on the Orb's location, sending Nebula and Gamora to the Cloud Tombs of Praxius under the command of his ally, the Kree 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 to Loki Thanos discovered that the Tesseract, the Space Stone, was on Earth, and allied himself with the exiled Loki, providing him a bladed scepter with one of the Infinity Stones embedded, and 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 both the scepter-laden Infinity Stone and the Tesseract transported to HYDRA and Asgard, respectively, 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
"The Orb is in my possession, as I promised." "Bring it to me." "Yes... that was our agreement. Bring you the Orb and you will destroy Xandar for me. However, now that I know it contains an Infinity Stone, I wonder what use I have for you."

- Ronan the Accuser and Thanos

Some time 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 Ravager member, Peter Quill. Unwilling to be denied another stone, Thanos ordered Ronan to pursue Quill and recover the stone, sending Gamora to aid the Kree in his pursuit.

Gamora found Quill first, cornering him on Xandar where he was attempting to sell the Orb. She recovered it, but what Thanos did not realize is that Gamora had chosen to cut all ties with him and now planned on handing the Orb over to the infamous Collector, Taneleer Tivan, who also sought the stones. When Ronan relayed news of Gamora's betrayal to Thanos, the Kree berated the Dark Lord for not taking the situation seriously and even murdered The Other when he lectured Ronan on not showing Thanos respect. Undaunted by The Other's death and Ronan's complaints, Thanos turned Ronan away, instructing him to return to his task and correct Gamora's betrayal, which he was only slightly irked by. He instructed Nebula to take Gamora's place as Ronan's aide in the endeavor.

Ronan and Nebula both eventually stole the Orb from Gamora, Quill, and their allies, but when Thanos was contacted by Ronan, he was furious to discover that the Kree, having experienced the power of the Orb firsthand, intended on keeping the Infinity Stone for himself. Nebula, contemptuous towards Thanos after the horror he forced her to endure throughout her youth, used this opportunity to betray him and join up with Ronan permanently. Now believing himself superior to Thanos, Ronan promised to come after the Dark Lord once he had finished Xandar. Unphased, Thanos cut contact with the pair without even putting in another word.

Ronan would eventually perish at the hands of Gamora and her companions, who gave the stone to the Nova Corps, making another Infinity Stone lost to Thanos.

Character Traits
Thanos is power hungry, searching for the Infinity Stones with the goal of controlling all of existence. He is sadistic and cruel, finding children that he can raise to be assassins and forcing them to watch as he murders their families. He is intimidating and frightening, with Ronan the Accuser showing visible signs of fear in his presence and Loki doing so at the mere mention of him, as well as being able to command the Chitauri army unchallenged. Thanos has an unforgiving nature; The Other warned Loki that he would know a new kind of pain if he did not give them the Tesseract, Thanos threatened to bathe the starways in Ronan's blood if he failed to deliver the Orb and forbade Gamora from rescuing Nebula when the latter fell into a trap whilst on a mission in the Cloud Tombs of Praxius. He has little to no regard for his followers, showing no empathy when Ronan killed The Other and referring to Gamora as his "favourite daughter" even with Nebula present. He inspires no love, as he is despised by his own "daughters" Gamora and Nebula. He is also manipulative and untrusting, sending Ronan to retrieve the Orb for him and not telling him that it contained an Infinity Stone. He keeps a low profile, lurking in the shadows and making others do his work for him.

Powers and Abilities
Thanos has not demonstrated his powers 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. Korath says he is the most powerful being in the universe, although Ronan was confident he could kill Thanos with the power of the Orb. Nevertheless, Thanos displayed no sign of concern after Ronan threatened him.

Allies and Subordinates

 * Loki - Ally
 * The Other † - Subordinate
 * Chitauri - Subordinates
 * Leviathans - Subordinates
 * Ronan the Accuser † - Former Subordinate
 * Korath the Pursuer † - Former Subordinate

Enemies

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

Behind the Scenes

 * Thanos' presence in The Avengers was kept top secret until the release of the movie.
 * Damion Poitier was credited as "Man 1" despite actually playing Thanos.
 * Josh Brolin was uncredited for his appearance in Guardians of the Galaxy.
 * Along with Bruce Banner, James Rhodes, Howard Stark and Fandral, Thanos is one of the few characters in the Marvel Cinematic Universe played by different actors in different movies.
 * Joss Whedon assisted James Gunn with the casting of Thanos.

Trivia

 * In the comics, Thanos was the master of the Infinity Gauntlet, which he used in the eponymous series in an attempt to court Death. He has no relationships with Loki nor the Chitauri, but he's nevertheless one of the Avengers' most historical foes. When he took a break from being a conqueror, Thanos was entrusted with the Reality Gem of the Infinity Gems.
 * The name "Thanos" is based on the name of the mythological Greek figure, meaning "death".
 * 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.