Calvin "Cal" Zabo, born Calvin L. Johnson, is a medical doctor of ambiguous morality. After being violently separated from his gifted wife and baby daughter by HYDRA and S.H.I.E.L.D., he started a quest to avenge his wife's "death" and find his daughter, committing numerous crimes that have caused others to consider him to be a monster. During this time, Zabo developed a formula that gave him enhanced strength. However, the side effects of the unstable formula gave Zabo an erratic personality and severe issues controlling his emotions, particularly anger.
After discovering his daughter's whereabouts, he made a temporary alliance with Daniel Whitehall's HYDRA branch so he could take his daughter to the ancient Kree City where she could fulfill her destiny. However, after the Terrigenesis, his daughter stayed with S.H.I.E.L.D., and Zabo formed a team of enhanced criminals to use them against S.H.I.E.L.D. This attracted the attention of the Inhumans, who kidnapped him and brought him to Afterlife where he was reunited with his wife. One more encounter with S.H.I.E.L.D. and HYDRA led to Zabo and his wife developing a plan to destroy S.H.I.E.L.D. once and for all, until Phil Coulson convinced him to fight his wife to protect his daughter.