- KADWALADR, JOHN (fl. second half of 18th century), ballad and interlude writer - see KADWALADR, SION
- KADWALADR, SION (fl. 1750-1765), writer of ballads and interludes
- KADWALADR, SIONYN (fl. second half of 18th century), ballad and interlude writer - see KADWALADR, SION
- KATHERYN of BERAIN (Mam Cymru, The mother of Wales; 1534/5 - 1591)
- KELSALL, JOHN (fl. 1683-1743), Quaker diarist
- KELSEY, ALFRED JOHN (1929 - 1992), association football player
- KEMBLE, ADELAIDE (1814? - 1879), singer - see KEMBLE, CHARLES
- KEMBLE, CHARLES (1775 - 1854), actor
- KEMBLE, FANNY (1809 - 1893), actress - see KEMBLE, CHARLES
- KEMBLE, FRANCES ANNE (1809 - 1893), actress - see KEMBLE, CHARLES
- KEMBLE, JOHN MITCHELL (1807 - 1857), philologist - see KEMBLE, CHARLES
- KEMEYS family Cefn Mabli,
- KEMEYS-TYNTE, Cefn Mabli - see KEMEYS
- KEMSLEY, 1st Viscount - see BERRY
- KENRICK family Wynn Hall, Bron Clydwr,
- KENRY, 2nd Baron - see WYNDHAM-QUIN, WINDHAM THOMAS
- KENSINGTON, Barons of - see EDWARDS
- KENTIGERN (518? - 603), saint, the founder of Glasgow
- KENWARD, JAMES (fl. 1868), writer and poet
- KENYON family Gredington, Peel Hall,
- KENYON, FANNY MARY KATHERINE - see BULKELEY-OWEN, FANNY MARY KATHERINE
- KEYNE (fl. late 5th century - early 6th century), saint
- KILMISTER, IAN FRASER (1945 - 2015), musician
- KILSBY - see JONES, JAMES RHYS
- KILVERT, ROBERT FRANCIS (1840 - 1879), cleric and diarist
- KINSEY, WILLIAM MORGAN (1788 - 1851), cleric and traveller
- KITCHIN, ANTHONY (1477 - 1563), bishop of Llandaff
- KNIBB, MARY (c.1798 - 1866), abolitionist and social reformer
- KNIGHT, ANNE BASSETT (1794 - 1825) - see KNIGHT, HENRY HEY
- KNIGHT, EDWARD DODDRIDGE (1806? - 1873) - see KNIGHT, HENRY HEY
- KNIGHT, HENRY HEY (1795 - 1857), cleric and antiquary
- KNIGHT, WILLIAM BRUCE (1785 - 1845), Welsh scholar, ecclesiastic, and administrator
- KOTSCHNIG, ELINED PRYS (1895 - 1983), psychoanalyst and pacifist
- KROCH, HEINZ JUSTUS (1920 - 2011), engineer and businessman
- KYFFIN, EDWARD (c. 1558 - 1603), cleric and composer of metrical psalms
- KYFFIN, MORRIS (c. 1555 - 1598), writer and soldier
- KYFFIN, RICHARD, dean of Bangor
- KYLSANT, Baron - see PHILIPPS, OWEN COSBY