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 secondary antagonists-turned-supporting protagonist (alongside Scarlet Witch) of Avengers: Age of Ultron.

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

Personality
Pietro is a rather cocky, arrogant, impatient, persuasive, treacherous, manipulative, unmerciful, tenacious, cunning, aggressive, cantankerous, indefatigable, and quick-tempered person. These personality traits are likely a side affect of his super-speed, due to thinking and acting at a much faster rate than most. Despite this, Pietro has a desire for peace as he wished to save his country to the point he was willing to be experimented on by HYDRA, giving him the formidable powers he now possesses.

He also deeply cares for Wanda and the two shared a deep bond though they would occasionally bicker like normal siblings. He looked after his sister and relied on her for support. Wanda was devastated by Pietro's death at the hands of Ultron, to the point she said to Ultron that she just "died".

Pietro originally desired to destroy the Avengers and in particular, Tony Stark for revenge, to the point they decided to join Ultron when he said he shared the same goal. However, Pietro chose to betray the A.I. when he found out about his true goal, showing that he is willing to put aside his personal grudges for the greater good.

Out of his relationships with the Avengers, his most complicated was with Hawkeye. Ever since they first met, the two had constantly competed, fought, and taunted each other. Though this initially started out as hatred, their relationship eventually becomes a friendly rivalry and they became good friends and teammates through Pietro helping the Avengers, while still continuing their friendly banter during the Battle of Sokovia. He later proves himself a true hero and Avenger by sacrificing his life to protect Hawkeye and a civilian boy from the Quinjet's gunfire. Hawkeye later named his newborn son, Nathaniel Pietro Barton, showing that he deeply respected Pietro for his choices.

Powers and Skills
He is able to run, move, react, and physically function at high levels of superhuman speeds. His super-speed give him the appearance of teleporting. He can charge his physical punches with super-speed, giving it the illusion of superhuman strength. He has displayed remarkable athletic and combat abilities during his fight against the Ultron Sentinels in Sokovia. He has also shown these abilities during the fight in South Africa.

Trivia

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