- THOMAS, EDWARD (1925 - 1997), champion boxer and an outstanding boxing trainer and a public figure in the life of Merthyr Tydfil
- THOMAS, EVAN (Ieuan Fardd Ddu; 1733 - 1814), printer and translator
- THOMAS, EVAN (Bardd Horeb; 1795 - 1867), poet and tailor
- THOMAS, EVAN (d. 1781) Cwmhwylfod, Sarnau, transcriber and owner of manuscripts
- THOMAS, EVAN (1804 - 1884), orthopaedic surgeon - see THOMAS, HUGH OWEN
- THOMAS, EVAN (1735 - 1814), bonesetter - see THOMAS, HUGH OWEN
- THOMAS, EVAN CAMBRIA (1867 - 1930), doctor and public health pioneer
- THOMAS, EVAN LORIMER (1872 - 1953), priest and scholar
- THOMAS, EVAN ROBERT (1891 - 1964), joiner and leader of the Welsh in Australia
- THOMAS, EVAN (c. 1710 - c. 1770), poet and boot-maker
- THOMAS, EZEKIEL (1818 - 1893), Calvinistic Methodist minister and author
- THOMAS, FRANCIS (Crythwr Dall o Geredigion; 1726 - 1796)
- THOMAS, FREDERICK HALL (Freddie Welsh; 1886 - 1927), light-weight boxing champion of the World
- THOMAS, GEORGE (1786 - 1859), writer of mock-heroic and satiric verse dealing with events in Montgomeryshire
- THOMAS, GEORGE GILBERT TREHERNE - see TREHERNE, GEORGE GILBERT TREHERNE
- THOMAS, GEORGE ISAAC (Arfryn; 1895 - 1941), musician and composer
- THOMAS, HELEN WYN (1966 - 1989), peace activist
- THOMAS, HENRY (1712 - 1802), Methodist exhorter and Independent minister
- THOMAS, HUGH (1673 - 1720), herald and antiquary
- THOMAS, HUGH EVAN (Huwco Meirion; 1830 - 1889), Independent minister
- THOMAS, HUGH HAMSHAW (1885 - 1962), palaeobotanist
- THOMAS, HUGH OWEN (1834 - 1891), orthopaedic surgeon
- THOMAS, HUMPHREY (1745 - 1805), schoolmaster - see THOMAS, DAVID
- THOMAS, IDRIS (1889 - 1962), minister (B)
- THOMAS, IDRIS - see JENKINS, ROBERT THOMAS
- THOMAS, IFOR (1877 - 1918), geologist and inspector of schools
- THOMAS, IFOR OWEN (1892 - 1956), operatic tenor, photographer and artist
- THOMAS, IORWERTH RHYS (1895 - 1966), politician
- THOMAS, ISAAC (1911 - 2004), minister (Independents) and college lecturer
- THOMAS, IVOR BULMER- - see BULMER-THOMAS, IVOR
- THOMAS, IVOR OWEN (1898 - 1982), Labour politician
- THOMAS, JAMES HENRY (1874 - 1949), politician and Labour leader
- THOMAS, JAMES LEWIS (1825 - 1904), architect and chief surveyor under the War Office - see THOMAS, JOHN EVAN
- THOMAS, JAMES PURDON LEWES (VISCOUNT CILCENNIN), (1903 - 1960), M.P.
- THOMAS, SIR JAMES WILLIAM TUDOR (1893 - 1976), ophthalmic surgeon
- THOMAS, JEFFREY (1933 - 1989), barrister and Labour\/SDP politician
- THOMAS, JENKIN (Siencyn Pen-hydd; 1746 - 1807), Methodist exhorter
- THOMAS, JENKIN - see THOMAS, SIENCYN (1690-1762)
- THOMAS, JOHN (1730 - 1804?), Congregational minister, and hymnist
- THOMAS, JOHN (1736 - 1769), cleric and antiquary
- THOMAS, JOHN (fl. 1689-1712), minister of the Tivy-side Independents
- THOMAS, JOHN (1646? - 1695), cleric
- THOMAS, JOHN (1691 - 1766), bishop of Salisbury
- THOMAS, JOHN (fl. 1719), poet
- THOMAS, JOHN (Eifionydd; 1848 - 1922), founder and editor of Y Geninen
- THOMAS, JOHN (1886 - 1933), chemist
- THOMAS, JOHN (1839 - 1921), musician
- THOMAS, JOHN (1821 - 1892), Independent minister, politician, and historian
- THOMAS, JOHN (Pencerdd Gwalia; 1826 - 1913), musician
- THOMAS, JOHN (Ifor Cwmgwys; 1813 - 1866), poet