Grant Ward
Agents of SHIELD really came into its own when – spoilers – Ward was revealed to be a secret HYDRA agent, later becoming a recurring enemy throughout the first three seasons.
Dr Fenhoff
Dr Fenhoff – a loose version of Dr Faustus from the comics – with his hypnotic, mind-control powers made for a formidable threat in the first season of Agent Carter.
Nebula
The MCU is terribly short on female villains so let’s be thankful for Nebula, that blue, cyborg assassin daughter of Thanos. She could rise up the list if she is given more to do in GotG Vol. 2.
Alexander Pierce
The Winter Soldier featured a perfectly cast Robert Redford as SHIELD turncoat Alexander Pierce as its surprise villain. The Butch Cassidy actor gave the film a real touch of class.
Dottie Underwood
The Black Widow known as Dottie Underwood (played by Bridget Regan) is a terrific match for Peggy Carter. It’s a real shame the show’s second season didn’t make more use of her.
Mariah Dillard
Cottonmouth and Diamondback might have been a bit disappointing, but Mariah Dillard (as played by Alfre Woodard) was a fascinating villain, with an interesting, political edge.
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