Final answer:
The theorist associated with the concepts of social interaction, ZPD, and 'I do, we do, you do' is Lev Vygotsky, known for his sociocultural theory of development.
Step-by-step explanation:
The theorist known for his theories that stress the fundamental role of social interaction in development, the concept of the Zone of Proximal Development (ZPD), and the learning approach commonly summarized as 'I do, we do, you do,' is Lev Vygotsky. Vygotsky's sociocultural theory of development posits that children learn and develop through interactive experiences within their cultural contexts. His ideas contrast with those of Jean Piaget, who emphasized the individual's cognitive development, and Erik Erikson, who proposed the psychosocial theory of lifespan development. Thus, the correct answer to the question is 1) Lev Vygotsky.