Doug Turnbull is an expert in search technology and relevance engineering, currently serving as Principal Engineer at Daydream, where he builds hybrid search systems combining lexical and vector retrieval, and develops LLM-driven quality programs for e-commerce search. Previously, he led machine-learning-driven search initiatives at Reddit, significantly improving search relevance through Learning to Rank methods. Doug also advanced e-commerce search at Shopify and served as CTO at OpenSource Connections. He co-authored the influential book Relevant Search (Manning, 2016) and created popular open-source tools, including Quepid and the Elasticsearch Learning to Rank plugin. He regularly speaks at industry conferences, making search relevance accessible to engineers.