Who he is: Calvin Zabo, a.k.a. Calvin Johnson, a.k.a. The Doctor
His power: Zabo is infected by a formula that grants him periodic superstrength; unfortunately, it also has a tendency to turn him into an uncontrollable rage monster, sort of like a less powerful, less indestructible Hulk. (Also, he only morphs body type a little bit, as opposed to full-on green machine transformation.)
His story: He’s first mentioned on Marvel’s Agents Of S.H.I.E.L.D. in season one, when S.H.I.E.L.D. antagonist Raina references “the Doctor” and is revealed in the episode “Beginning Of The End.” We soon learn that Zabo is the father of Daisy Johnson (then still known as Skye) and has been orchestrating events in order to reconnect with her. It’s gradually revealed that Zabo was separated from his Inhuman wife, Jiaying, and daughter back when Daisy was a child. Zabo treated himself with the formula that made him strong but volatile, only to learn S.H.I.E.L.D. took Daisy while Calvin was rescuing his wife from death at the hands of Hydra. After Daisy was taken, however, Jiaying divorced him, and Zabo changed his name, setting out on a mission of revenge.
He raised Raina, who helped him locate Daisy, and entered into a temporary alliance with Hydra leader Daniel Whitehall in order to get Daisy to undergo Terrigenesis and uncover her powers. After it succeeds, Zabo attempts to put his family back together at the Inhuman compound known as Afterlife, but Jiaying’s machinations to destroy S.H.I.E.L.D. end up with Calvin killing his wife to protect Daisy. As a result of the pain he’s suffered, Zabo undergoes a mind-wiping procedure and becomes a veterinarian. It’s way more peaceful than his old life.
Played by: Kyle MacLachlan
Currently, Calvin is: Living an ignorant but much gentler existence as a vet doctor.
Where will we see him next? It’s unknown if he’ll pop back up for a cameo again anytime.