Final answer:
The earliest agent of socialization is the family, as it introduces the individual to societal norms and behaviors from birth.
Step-by-step explanation:
The earliest agent of socialization for an individual is typically the family. Socialization is the process through which individuals learn values, norms, and behaviors that are appropriate for members of their society.
From the moment of birth, the family plays the crucial role of introducing the child to social norms, language, and the basic behavioral patterns necessary for functioning in society.
Unlike the school, mass media, or workplace options in the question, the family is the primary context in which early socialization occurs, shaping the character, beliefs, and social skills of the child from an early age before other agents like schools take an influential role.