Hernandez was one of the first "new style" black screen actors, who neither sang nor danced but played characters just as white actors did. He grew up in Rio de Janeiro. In 1922 he first began performing onstage, working in an acrobatic act. Later he lived in the Caribbean and worked as a professional boxer under the name Kid Curley. He went on to work in a minstrel show, in circuses, and in vaudeville. He debuted on Broadway in 1927 in Show Boat. He played a few bit parts in the black audience-targeted films of Oscar Micheaux, and also worked as a radio scriptwriter. He broke through as a screen actor in Intruder in the Dust (1949), in which he played a proud black man wrongly accused of having killed a white Southerner. He played masculine, sensitive, individualistic men. After getting a number of solid roles, he was obliged to accept lesser roles in most of the films he made from the late '50s on. He continued acting until shortly before his death, working in both films and on TV.