Quick Silver has the mutant ability of a super human speed and could even travel by foot at a speed at even exceeds the speed of sounds for hundreds of miles before tiring. He can fly in short distance by just flapping his legs and his arms. He was trained by Captain America in hand to hand combat.Source here
image sourceHis real name is Pietro Django Maximoff and he is the twin brother of Scarlet Witch. In some other stories in comics , he was a son of Magneto and the half-brother of Polaris.
Aside from having a super speed ability he can also speak and think in supersonic speed also with a very enhanced stamina and durability. Even he has a very super human fast reflexes.He had joined a lot of Super Hero teams, not just Avenger.