- "I've got this completely under control!"
- ―Sif, Thor: The Dark World.
Sif is an Asgardian warrior and Thor's childhood friend.
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. 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. Back in Asgard, Sif brings Heimdall to the Restore Room, while Thor defeats Loki once and for all.
Sif saw Loki's treachery and risked all to return Thor to Asgard but on Earth, she saw that she had lost Thor's heart to another. The human Jane Foster. Now at the end of a long campaign to free the Nine Realms from strife, Sif tries to rekindle her relationship with Thor.
Sif possesses superhuman physical attributes such as strength, stamina, speed and reflexes and is an incredibly skillful fighter. She uses a double edged spear.
She is portrayed by Jaimie Alexander. Alexander admitted that shes was already very familiar with Marvel Comics before taking the part having grown up with four brothers. Alexander said the part required hours a day in the gym, though training is not unfamiliar to her, explaining she was one of few girls on her Colleyville, Texas, high-school wrestling team. Alexander described her character as "one of the guys" and that, "She's a very talented, skilled warrior and can stand on her own against any villain in the film". About her relationship with Thor she stated, "She is very loyal to Thor and cares a lot about protecting him and protecting Asgard".