Which author’s work often explores themes of isolation and social criticism?

The choice of Joseph Conrad as the correct answer is well-founded, as his literary works frequently delve into themes of isolation and social criticism. Conrad's narrative style and subject matter often reflect the inner struggles of individuals against the backdrop of societal expectations and the complexities of human relationships.

For instance, in novels like "Heart of Darkness," Conrad examines the isolation experienced by characters in hostile environments, while also critiquing imperialism and the moral failures of colonial enterprises. His characters are often portrayed grappling with their own alienation, both from society and from themselves, leading to a profound exploration of existential themes and the critique of societal norms.

Authors such as James Fenimore Cooper, Thornton Wilder, and Sophocles do touch upon social themes, but their focus differs significantly from the pervasive isolation and moral ambiguities that define Conrad's narratives. Cooper’s works primarily focus on themes related to the American frontier and nature. Wilder often explores human relationships and community dynamics in a more optimistic light, while Sophocles concentrates on tragedy and fate in a historical and mythological context rather than the modern social critique that Conrad embodies. Thus, Conrad’s distinctive blend of isolation and social commentary makes him the most fitting answer in this instance.