Bill was more than an SEO, he was a mentor and an educator. His insights on Search Engines, Information Retrieval and technical SEO were fathomless and his analyses and contextualisation of Google patents should be required reading for any serious SEO professional. If there will ever be an academic SEO curriculum, Bill's blow, SEO by the Sea will certainly serve as the coursebook.
I honestly believe there is not a single SEO professional working in the field today that hasn't been influenced by Bill Slawski. The term "influencer" gets tossed around quite a lot, but no man in our industry deserved this distinction more literally than Bill.
He was a tremendous SEO professional, an incredible mind and a fantastic human being. I am honoured to have made his acquaintance and I am deeply saddened by the news of his passing. The SEO world has truly lost one of its titans today.