Others
- William ap Thomas (died 1445), Welsh soldier and sheriff
- William Bevil Thomas (1757–1825), Newfoundland merchant and land developer
- William Davies Thomas (1889–1954), Welsh academic
- William Henry Griffith Thomas (1861–1924), English clergyman
- William Luson Thomas (1830–1900), English wood engraver and newspaper founder
- William Fitz Thomas (fl. 1400s), Irish judge
- "William Thomas", an alias of Wilhelm Thomas, who gained notoriety in the Adolph Beck case
- William Thomas (architect) (1799–1860), Anglo-Canadian architect
- William Thomas (bishop) (1613–1689), bishop of Worcester
- William Thomas (cleric) (1734–1799), Welsh priest and scholar
- William Tutin Thomas (1829–1892), his son, also an architect
- William Thomas (activist) (1947–2009), American anti-nuclear activist
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