Thanos

"You think you know pain? He will make you long for something sweet as pain!"

- The Other

Thanos is an extraterrestrial warlord who allies himself with Loki.

Thor: The Dark World Prelude
Frigga, the adoptive mother of Loki, observed the meeting between Loki, Thanos and The Other.

The Avengers
Thanos is a powerful alien, a warlord who rules over a dead dimension. He allies himself with the exiled Loki Laufeyson, providing him with the deadly army of the Chitauri, who will help him conquering Earth, in exchange for the Tesseract, a powerful energy source.

When Loki has arrived on Earth, Thanos is contacted by him, and the Other warns the God of Mischief of the price of failure and reminding him to not question the will of the master, declaring that if he fails in defeating the Earthlings, Thanos will make him know a new kind of suffering.

When eventually Loki is defeated, the Other complains that the Earth's inhabitants are not as weak as they were supposed to be and declares that challenging the Earth's heroes would be to court Death. To this, Thanos simply smiles.

Guardians of the Galaxy
To be added

Character traits
Thanos is one of the most powerful beings of the universe, and even though none of his powers are actually shown (yet), he was able to threaten a god such as Loki and command the powerful army of the Chitauri unchallenged.

Relationships

 * Loki Laufeyson - Ally.
 * The Other - Subordinate.
 * Chitauri - Subordinates.
 * Leviathans - Subordinates.
 * Nebula - Granddaughter

Appearances/Actors

 * Marvel Cinematic Universe (2 films)
 * The Avengers (First appearance) - Damion Poitier
 * Guardians of the Galaxy - TBA
 * Marvel Cinematic Universe (1 comic)
 * Thor: The Dark World Prelude

Behind the scenes

 * Thanos' presence in the movie has been kept top secret from the production until the very release of The Avengers.
 * Damion Poitier was credited as playing "Man #1" in order to hide the identity of Thanos at the end of the film. It was later publicly announced after the film's release.
 * Kevin Feige has said that Thanos will likely be played by a different actor in future films.
 * Joss Whedon has said that Thanos will play a major role in the "Final Act", referring to either the final act of Avengers: Age of Ultron or Avengers 3 as a whole.

Trivia

 * In the comics, Thanos has no relationships with Loki Laufeyson nor the Chitauri, but he's nevertheless one of the historical foes of the Avengers.
 * In the comics, Thanos is the master of the Infinity Gauntlet, which he used in the eponymous series in an attempt to court Death.
 * Thanos is one of few major antagonists not to be killed in their debut appearance, others being The Other, Loki, and The Abomination.