Wen-tau Yih
Making the retrieval step inside retrieval-augmented systems good enough that the generation step has something to work with.
Long before RAG existed as a term, Yih was building the retrieval substrate it depends on. Dense Passage Retrieval (2020) is the paper that made dense-vector search competitive with traditional inverted-index methods for open-domain QA — virtually every modern RAG system descends from that result, including the ones that don't credit it. Reading Yih is the cleanest way to understand why the retrieval in retrieval-augmented generation is usually where systems silently break, and why FActScore (which he co-authored) bothers to score atomic facts against an external knowledge source rather than against the model's parametric memory.