Who was the father of social constructivism?

Social constructivism is a theory of learning holding that knowledge and cognitive development are not built by an individual mind acting alone, but are actively co-constructed through social interaction, language, and participation in a cultural context — the social environment is the primary engine of intellectual growth, not merely a backdrop to it.

Lev Vygotsky developed this position most fully in his sociocultural theory of development. He proposed that higher mental functions originate in social interaction before becoming internalised by the individual, and introduced the Zone of Proximal Development to describe how a learner's capabilities expand through guided interaction with more knowledgeable others — a teacher, a parent, a peer — rather than through solitary discovery. Because he placed the social and cultural mediation of learning at the very centre of cognitive development, Vygotsky is recognised as the father of social constructivism.

Each of the other named theorists is linked to a different, non-social account of how understanding is built:

• Novak is known for concept mapping, a diagrammatic technique for organising ideas into a hierarchy of linked propositions — a study and representation tool, not a theory of how development itself occurs.

• Piaget proposed cognitive constructivism: a child moves through four fixed stages of development mainly by acting on and reasoning about the physical world, with social interaction playing only a secondary role.

• Glasersfeld proposed radical constructivism: an individual mind actively builds its own model of experience, and that model can never be checked against an external reality — the emphasis stays on the individual knower rather than the social process.

Since the question asks specifically for the figure behind SOCIAL (interaction-driven) constructivism, the answer is Vygotsky.