Academia
- William A. V. Clark, New Zealand-born American geographer, member of the American National Academy of Sciences
- William Bell Clark (1889–1968), American advertising executive and naval historian
- William Bullock Clark (1860–1917), American geologist
- William C. Clark (born 1948), American ecologist and environmental policy analyst, member of the American National Academy of Sciences
- William D. Clark (1916–1985), economist and first director of the Overseas Development Institute
- William George Clark (1821–1878), British scholar of Shakespearean literature
- William Robinson Clark (1829–1912), Canadian theologian
- William S. Clark (1826–1886), American scholar and Massachusetts educator
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