With the release of a new trailer for Marvel's Thunderbolts*, I'm now positive who the antagonist will be. Lewis Pullman's "Bob" appears to be the MCU's Robert Reynolds, also known as The Sentry, based on the first teaser for the upcoming team-up film. Despite being one of the most formidable and formidable heroes in the whole Marvel Universe in the original comics, Sentry has a very sinister side that appears to be present in Thunderbolts* as well.
Val, played by Julia Louis-Dreyfus, confirms that "The Avengers are not coming" in the latest teaser for Marvel's Thunderbolts*. In light of this, it seems that she and Bucky Barnes will be putting up a new squad of agents, which will include Yelena Belova, red Guardian, Taskmaster, Ghost, U.S. Agent, and a newbie named Bob. Even though there was a lot of speculation from the initial teaser, this new Thunderbolts* trailer has me persuaded that Bob is The Sentry and that the primary antagonist of the movie will be the key Marvel character.
Lewis Pullman's Bob appears to be the silhouetted character wearing a full suit and cape, even if he is kept in the background for the entirety of this new teaser. This undoubtedly lends credence to the notion that Bob is, in fact, Robert Reynolds, also known as The Sentry, a superhero who mostly appears in comics with a blue cape and yellow suit. However, this new teaser for the forthcoming MCU film does not portray him as a hero.
In the new Thunderbolts* teaser, New York City appears to be engulfed in a significant darkness that appears to be coming from the Sentry himself. These Sentry victims, who are seen deleting citizens who are escaping for their lives, are reduced to shadows as the darkness appears to be expanding and engulfing an increasing portion of the city, which will surely be the main menace in the next team-up film. Accordingly, this appears to be connected to Sentry and the sinister side of his enormous power.