Quicksilver (Marvel Cinematic Universe)

"You didn't see that coming?"

- Quicksilver's most famous quote

Quicksilver (real name: Pietro Maximoff) is a minor character in Captain America: The Winter Soldier and one of the two tertiary antagonists turned supporting protagonist of Avengers: Age of Ultron.

He is portrayed by Aaron Taylor-Johnson ,who is best known for portraying another superhero by Marvel ,Kick-Ass.

Captain America: The Winter Soldier
Pietro and his sister, Wanda Maximoff, appeared in the mid-credits scene as test subjects in an experiment for HYDRA.

The Avengers: Age of Ultron
Pietro makes his first appearance along with his sister, Wanda, at the beginning of the movie during the Avenger's attack on the HYDRA base in Sokovia. He, along with his sister, go out to try to fight them, with he going after Hawkeye. He manages to hold them off but fails at keeping them from infiltrating the base.

After HYDRA's branch in Sokovia falls, Pietro and Wanda eventually are sought after and join the newly-born Ultron. Due to their parents being killed by a weapon labled "Stark" (Stark Industries being owned by Iron Man), the two are originally very willing to assist Ultron in trying to wipe out the Avengers. Their first major conflict with them occurs after they follow Ultron to Wakanda to obtain a stash of vibranium located there in order to construct a new body for Ultron. The twins are sent in first. When it becomes clear that they won't be able to obtain the rare metal, Ultron himself intervenes while the twins are sent to intercept the just-arrived Avengers. They're able to fight them long enough for Ultron to obtain the material, although Pietro has to save his sister when her attack on Hawkeye is ineffective. They then escaped the base, but not before Wanda sent the Hulk into a rampage.

The two later follow Ultron to Seoul, South Korea. There, Ultron planned to take advantage of Dr. Helena Cho's regeneration "Cradle" to, with the vibranium, create the ultimate form for Ultron to use. As Ultron is uploading his conciousness into the body, however, Wanda disovers she's able to suddenly read Ultron's mind. When discovering that Ultron plans to wipe out all of humanity, they put aside their grudge and run off to help the Avengers.

Ultron followed the two out, providing the opening for the Avengers to steal the Cradle. A fight ensures, with the Avengers retreating to New York with the Cradle and the Maximoff twins while Ultron proceeds to Sokovia for the final phase of his plan. After witnessing the birth of The Vision, the Avengers travel to Sokovia to engage in the final battle with Ultron.

Once there, it is revealed that Ultron plans to use a device to levitate a large portion of Sokovia into the air and then drop it from an extreme height, causing a global extinction. The Maximoffs are responsible for blocking the device from Ultron and his army while the other Avengers attempt to evacuate the area while simultaneously fighting Ultron. While grabbing a child, one of the last evacuees, Hawkeye is targeted by Ultron. Pietro runs and jumps in front of them, killing him and saving them. His sacrifice indirectly helps defeat Ultron, as Wanda's anguish manifests her telekinesis in a way that kills most of Ultron's army.

In remembrance, Hawkeye's newborn son is given the middle name "Pietro" (his first name had already been chosen as Nathaniel in honor of Hawkeye's best friend, Natasha Romanov/Black Widow.)

Trivia

 * He is played by Aaron Taylor-Johnson who also played another superhero: Kick-Ass.
 * His alias 'Quicksilver' was never mentioned in the film.