Questions: needs the most influential theorist to discuss the importance of adolescent friendships, proposed that friends become increasingly important in meeting social needs in adolescence.

The answer is Harry Stack Sullivan.

James Marcia is known for his work on identity development, particularly his theory of identity statuses. While his work is influential in understanding adolescent development, it does not specifically focus on the importance of friendships.

Harry Stack Sullivan is a prominent figure in the field of interpersonal theory. He emphasized the significance of interpersonal relationships and posited that friendships become increasingly important during adolescence. According to Sullivan, these relationships are crucial for meeting social needs and play a vital role in the development of self-concept and identity.

Jean Piaget is renowned for his theory of cognitive development, which outlines how children's thinking evolves in stages. Although his work is fundamental in understanding cognitive development, it does not specifically address the importance of adolescent friendships.

Erik Erikson is famous for his theory of psychosocial development, which includes stages that span from infancy to adulthood. While Erikson's stages do touch on social relationships, his work is broader and does not focus specifically on the role of friendships in adolescence.

Therefore, the most influential theorist who discussed the importance of adolescent friendships is Harry Stack Sullivan.