Sif

"I've got this completely under control!" "Is that why everything is on fire?!"

- Sif and Thor

Sif is the Asgardian goddess of war and a good friend of Thor and the Warriors Three. She is also known as Lady Sif.

Early life
"And who proved wrong all who scoffed at the idea that a young maiden could be one of the fiercest warriors this realm has ever known?" "I did!" "True, but I supported you, Sif."

- Thor and Sif

Not much is known about Sif's early life. But, it is known that, thanks to her friend Thor, who believed in her capabilities, she became one of the most appreciated warriors of Asgard, along with the Warriors Three, Loki, and Thor, himself. At some point, Sif was briefly involved with a warrior named Haldorr, who was later enthralled by the sorceress Lorelei. The event led to Haldorr's death, creating a deep hatred between Sif and Lorelei.

Jotunheim
"This isn't like a journey to Earth, where you summon a little lightning and thunder, the mortals worship you as a God! This is Jotunheim." "My father fought his way into Jotunheim. Defeated their armies and took their casket! We would just be looking for answers." "It is forbidden!"

- Fandral, Thor, and Sif

When the Frost Giants of Jotunheim interrupted Thor's coronation ceremony by attempting to steal the Casket of Ancient Winters, Sif, Loki, and the Warriors Three were convinced by Thor to attack Jotunheim, to find those responsible. While in Jotunheim, Sif fought alongside her friends against an army of Giants led by Laufey himself, and managed to slain many of them, but was forced to flee when they were outnumbered. Eventually, the team was saved by Odin himself, who intervened to prevent their killing. Helpless, Sif assists to Thor's banishment on Earth.

Disobeying the King
"We all know what we have to do." "We must go. We must find Thor." "It's treason." "To hell with treason. It's suicide."

- Sif, Hogun, Fandral, and Volstagg

Some days later, Sif persuades the Warriors Three to ask Odin to recall Thor back home, but when they arrive in the throne room, they find Loki sitting as the new ruler of Asgard, as a substitute to Odin who's fallen into Odinsleep. Loki denies their request to call his stepbrother back, but they decide to ignore his order and to go to Midgard anyway.

Battle on Earth
"You know I can't go home. My father is...dead because of me. I must remain in exile." "Thor, your father still lives."

- Thor and Sif

Heimdall agrees with them and opens Bifrost Bridge for them, and the four gods arrive on Earth, in New Mexico. Here, they easily spot Thor, and find out that he's been tricked by Loki's lies. Briefly later, The Destroyer is sent to Earth by Loki to kill Thor and the other Asgardians, and Sif engages it in battle with her friends. While the Warriors Three buy her some time, Sif climbs a rooftop and attacks the Destroyer from above, piercing its troath with her spear. Immediately after, anyway, the Destroyer regenerates itself and almost vaporizes her with his energy blast. Sif flees with her companions, leaving Thor, who claims to have a plan, behind, but only to assist his sacrifice and his rebirth in his divine form.

Return to Asgard
"My Queen, I'm so sorry for your loss. How is he?" "He mourns for his brother. And...he misses her, the mortal."

- Sif and Frigga about Thor

Back in Asgard, Sif brings Heimdall to the Restore Room, while Thor defeats Loki once and for all.

Along with other Asgardians, Sif celebrates Odin's return to the throne and Thor's return in the realm, participating to a gargantuan banquet.

War for the Realms
"Betray him, and I will kill you." "Nice to see you too, Sif.""

- Sif and Loki

Sif is present during the battle against the Marauders on Vanaheim. During the fight, she saves Thor's life when the Marauders attempted to fire a missile at Thor's head, only for Sif to block it with her shield. Sif later attempts to renew a romantic relationship with Thor, secretly jealous of his love for Jane Foster. She later participated in the battle against Malekith and the Dark Elves, which ended in Frigga's death at the hands of Algrim. Shortly thereafter, Sif aided Thor in freeing Loki and getting them and Jane off of Asgard and into Svartalfheim.

Transfer of the Aether
After the Battle of Greenwich, the Aether was recovered from Svartalfheim and contained. Due to the fact that the Tesseract is already on Asgard, it would be unwise to keep two Infinity Stones in the same place, so Sif and Volstagg deliver the Aether to the Collector.

Hunt for Lorelei
"You are of S.H.I.E.L.D.?" "Yeah...?" "I am Lady Sif, of Asgard. Your world is in grave danger."

- Sif and Grant Ward

Some time after the defeat of Malekith, Lorelei escaped from imprisonment, and Sif is tasked with capturing her. Sif pursues her to Earth, where she is immediately greeted by Phil Coulson's team of elite S.H.I.E.L.D. agents. Together, the two parties track Lorelei, but in the ensuing confrontation, Lorelei manages to take control of S.H.I.E.L.D Agent Grant Ward and uses him to attack Coulson and his team but is defeated nontheless thanks to the combined efforts of the team and Sif and despite her urges to kill Lorelei as the latter taunts her about how Thor will never show intrest in her Sif lets her live and after thanking Coulson and his team for their help departs with Lorelei and returns to Asgard.

Personality
Being the only female warrior in Asgard, Sif is very proud and always eager to prove herself. She's the closest of friend with Thor and the Warriors Three, and she's an honorable warrior on the battlefield. She often is independent and uneasy in following the orders.

Powers and Abilities
As an Asgardian, Sif possesses superhuman physical attributes such as strength, stamina, speed and reflexes, and she's an incredibly skillful fighter. She wields a double edged spear, which she uses perfectly, either separate as two blades or a single long sword staff.

Powers
Sif possesses all of the various superhuman attributes common among the Asgardians. Sif possesses superhuman strength, speed, agility, reflexes, durability, and is extremely long-lived.
 * Asgardian Physiology: As an Asgardian, Sif has superhuman abilities.
 * Superhuman Strength: Like all Asgardians, Sif is super-humanly strong and possesses greater physical strength than the average Asgardian female. She was able to hold her own against many stronger foes.
 * Superhuman Speed: Sif is capable of running and moving at speeds much greater than that of even the finest human athlete.
 * Superhuman Stamina: Sif's musculature produces considerably less fatigue toxins during physical activity than the musculature of a human being.
 * Superhuman Dense Tissue: Sif's bodily tissues are denser than the tissue of a human. As a result, Sif is actually much heavier than she appears. This increased tissue density also contributes somewhat to her physical strength.
 * Superhuman Durability: Sif's body is much more resistant to physical harm than the body of a human being. She is capable of withstanding great impact forces from Frost Giants and the Destroyer, and exposure to extreme temperatures and pressures of Jotunheim.
 * Regenerative Healing Factor: Despite her body's resistance, Sif can be injured like any other Asgardian. However, her metabolism enables her to rapidly regenerate damaged bodily tissue with greater speed and efficiency than a human being is capable of. Injuries such as slashes and punctures can fully heal within hours, whereas broken bones can heal within a few days. However, she isn't able to regenerate severed limbs or missing organs. After Sif and the Warriors Three took a severe beating from the Destroyer, she returned to Asgard looking no worse for ware.
 * Extended Longevity: Like all Asgardians, Sif ages at a rate that is much slower than that of a human being. However, Asgardians aren't completely immune to aging, as she is several hundred years old by human standards.

Abilities
Sif is a formidable combatant and has received extensive training in unarmed combat and swordsmanship. Asgard's greatest warrior Thor comments that Sif proved "all wrong who scoffed at the idea of a young maiden being one of the fiercest warriors."

Equipment

 * Double-bladed Sword: Sif's signature weapon of choice is a double-bladed sword. One of the two blades is retractable, allowing for Sif to fight with a single-blade.
 * Shield: Sif almost always carries around a shield, providing defense in battle. The shields are made up of a strong Asgardian metal capable of deflecting gunfire.
 * Armor
 * First Set: Sif’s first armor consisted of a collared red mini-dress over chain mail and was covered with silver plating. The silver plating was in the shape of a deep-scoop shirt with her upper chest covered by silver chain mail. It also was in the form of a belt and shoulder pads. Her right upper arm had a silver bracelet and her left arm had a red band around it. Her hands and lower arms were covered by red fabric and her arms had arm-bracers. Sif wore dark-grey pants and detailed black boots. This armor was worn with a pale greyish-purple cloak during her visit to Jotunheim.
 * Second Set: Sif’s second armor was silver and dark red. Her armor wore a red leather dress that continued down her torso ending in a multi-paneled mini-skirt. Over her dress, she wore silver armor plates that ended right above her cleavage. Her neck was covered by a sheer material. Sif also wore black pants under her skirt and brown and silver knee high boots.

Friends and Allies

 * Thor
 * Odin
 * Frigga
 * Heimdall
 * Warriors Three
 * Fandral
 * Volstagg
 * Hogun
 * Haldorr † - Lover
 * Coulson's Team
 * Phil Coulson
 * Grant Ward
 * Melinda May
 * Leo Fitz
 * Jemma Simmons
 * Skye

Enemies

 * Loki
 * The Destroyer
 * Laufey
 * Frost Giants
 * Marauders
 * Lorelei

Video game only

 * Fire Demons

Behind the scenes

 * In the non-canon comic Captain America & Thor: Avengers! Sif helps her friends to free Fandral who is captured by the Dark Elves led by Queen Alflyse.

Trivia

 * In Marvel Comics, Sif is Thor's lover and main love interest, not just a friend or a teammate. Her feelings for Thor are hinted in the end of the movie when she looks at him talking with his father.
 * In Norse mythology, Sif is the wife of Thor.
 * Also in the comics, Heimdall and Sif are brother and sister. This relationship has not been explored in the movies.