Concept:
Gender performativity is an important idea in gender studies and feminist theory.
Step 1:
Gender performativity means gender is not something people are born with, but something repeatedly performed through actions and behaviour.
Step 2:
This concept was proposed by feminist theorist Judith Butler.
Step 3:
Butler argued that social behaviours, language, dress, and actions continuously construct gender identity.
Step 4:
• G.H. Mead worked on symbolic interactionism.
• Sylvia Walby studied patriarchy.
• Nancy Chodorow focused on psychoanalytic feminism.
Step 5:
Hence, the correct answer is Judith Butler.
\[
\boxed{\text{(2) Judith Butler}}
\]