- WILLIAMS, OWEN (GAIANYDD) (1865 - 1928), Calvinistic Methodist minister, and author
- WILLIAMS, OWEN (1774 - after 1827), musician
- WILLIAMS, OWEN HERBERT (1884 - 1962), surgeon and Professor of Surgery
- WILLIAMS, PENRY (1800 - 1885), painter
- WILLIAMS, PETER (Pedr Hir; 1847 - 1922), Baptist minister, author, and eisteddfodwr
- WILLIAMS, PETER (1723 - 1796), Methodist cleric, author, and Biblical commentator
- WILLIAMS, PETER (1756 - 1837), cleric and author
- WILLIAMS, PETER BAILEY (1763 - 1836), cleric and writer
- WILLIAMS, PHILIP (d. 1717), genealogist
- WILLIAMS, PRYSOR - see WILLIAMS, ROBERT JOHN
- WILLIAMS, Sir RALPH CHAMPNEYS (1848 - 1927), governor of Newfoundland - see WILLIAMS, JAMES
- WILLIAMS, RAYMOND HENRY (1921 - 1988), lecturer, writer and cultural critic
- WILLIAMS, Sir RHYS - see RHYS-WILLIAMS, Sir RHYS
- WILLIAMS, RICHARD (fl. 1790?-1862?), a writer and singer of ballads
- WILLIAMS, RICHARD (1835 - 1906), antiquary and lawyer
- WILLIAMS, RICHARD (Gwydderig; 1842 - 1917), collier and poet
- WILLIAMS, RICHARD (1802 - 1842), Calvinistic Methodist minister, and author
- WILLIAMS, RICHARD (1747 - 1811), cleric and man of letters
- WILLIAMS, RICHARD (d. 1724), Baptist minister
- WILLIAMS, RICHARD (Dryw Bach; 1790 - 1839), poet and singer
- WILLIAMS, RICHARD HUGHES (Dic Tryfan; 1878? - 1919), journalist and short story writer
- WILLIAMS, ROBERT (1810 - 1881), cleric, Celtic scholar and antiquary
- WILLIAMS, ROBERT (Robert ap Gwilym Ddu; 1766 - 1850), poet
- WILLIAMS, ROBERT (Trebor Mai; 1830 - 1877), poet
- WILLIAMS, ROBERT (1782 - 1818), composer of the hymn-tune 'Llanfair'
- WILLIAMS, ROBERT (1848 - 1918), architect, author and social reformer
- WILLIAMS, ROBERT (1804 - 1855), Wesleyan minister - see WILLIAMS, THOMAS
- WILLIAMS, ROBERT (fl. 1836), poet - see WILLIAMS, THOMAS
- WILLIAMS, ROBERT - see WILLIAM, ROBERT
- WILLIAMS, ROBERT ARTHUR (Berw; 1854 - 1926), cleric and poet
- WILLIAMS, ROBERT DEWI (1870 - 1955), minister (Presb.), headmaster of Clynnog School and writer
- WILLIAMS, ROBERT HERBERT (Corfanydd; 1805 - 1876), musician
- WILLIAMS, ROBERT JOHN (PRYSOR; 1891 - 1967), collier and actor
- WILLIAMS, ROBERT ROLFE (1870 - 1948), a pioneer of Welsh-medium education
- WILLIAMS, Sir ROGER (1540? - 1595), soldier and author
- WILLIAMS, ROGER (1667 - 1730), Independent minister
- WILLIAMS, ROWLAND (1779 - 1854), cleric
- WILLIAMS, ROWLAND (Hwfa Môn; 1823 - 1905), Independent minister, and archdruid of Wales
- WILLIAMS, ROWLAND (1817 - 1870), cleric and scholar
- WILLIAMS, Sir ROWLAND LOMAX BOWDLER VAUGHAN (1838 - 1916), judge - see WILLIAMS, JOHN
- WILLIAMS, SAMUEL (c. 1660 - c. 1722), cleric and author
- WILLIAMS, STEPHEN JOSEPH (1896 - 1992), Welsh scholar
- WILLIAMS, STEPHEN WILLIAM (1837 - 1899), engineer, architect, and antiquary
- WILLIAMS, TALIESIN (1787 - 1847), poet and author
- WILLIAMS, THOMAS (Gwilym Morgannwg; 1778 - 1835), poet
- WILLIAMS, THOMAS (Clwydfro; 1821 - 1855), poet
- WILLIAMS, THOMAS (Hafrenydd; 1807 - 1894), musician
- WILLIAMS, THOMAS (Soranus; 1818 - 1865), physician and scientist
- WILLIAMS, THOMAS (Eos Gwynfa, Eos y Mynydd; c. 1769 - 1848), poet
- WILLIAMS, THOMAS (Twm Pedrog; 1774 - 1814), poet