- ISAAC, DANIEL (fl. diwedd y 18fed ganrif), gweinidog y Bedyddwyr - gweler WINTER, CHARLES
- ISAAC, DAVID LLOYD (1818 - 1876), clerigwr a llenor
- ISAAC, EVAN (1865 - 1938), gweinidog Wesleaidd
- ISAAC, JACOB, gweinidog y Bedyddwyr - gweler WINTER, CHARLES
- ISAAC, JACOB - gweler WINTER, CHARLES
- ISALAW - gweler RICHARDS, JOHN
- ISFOEL - gweler JONES
- ISGARN - gweler DAVIES, RICHARD
- ISHMAEL (fl. 6ed ganrif), sant
- ISHMAEL - gweler ISFAEL
- ISLWYN - gweler THOMAS, WILLIAM
- ISLWYN, Barwn - gweler HUGHES, ROYSTON JOHN
- ISNANT - gweler HARKER, EDWARD
- ITHEL ap RHOTPERT neu ROBERT (fl. 1357-82), archddiacon
- ITHEL DDU (fl. c. 1300-40), bardd
- IVON - gweler JONES, JOHN
- IWAN - gweler WILLIAMS, DAVID