Taskmaster

In the comics, Taskmaster is Tony Masters, a former shield agent with "photographic reflexes," letting him perfectly mimic any fighting style or skill he sees performed even once. That makes him a challenging foe for the Avengers since he can use Captain America's shield-throwing, Black Panther's claw fighting, and Hawkeye's archery all equally well. While Black Widow may have shed some of Taskmaster's comic book visuals, the new trailer shows that his ability to imitate the Avengers made the transition without issue. The cinematic Taskmaster's identity remains a secret.

According to the synopsis, "In Marvel Studios' action-packed spy thriller Black Widow, Natasha Romanoff aka Black Widow confronts the darker parts of her ledger when a dangerous conspiracy with ties to her past arises. Pursued by a force that will stop at nothing to bring her down, Natasha must deal with her history as a spy and the broken relationships left in her wake long before she became an Avenger."