Ieuan Cennydd Evans is a former Welsh rugby union player, known for his career as a wing for Wales and the British and Irish Lions. Born in Pontarddulais, Wales, Evans began his rugby journey at a young age and went on to achieve significant milestones in his career. Playing 232 games and scoring 194 tries for Llanelli, he later joined Bath and played for the Hong Kong Football Club. On the international stage, Evans earned 72 caps for Wales, scoring 33 tries and earning the nickname "Merlin." Notable highlights include captaining Wales to victory in the Five Nations Championship and his contributions to the British and Irish Lions tours. Recognized for his contributions to rugby, Evans was awarded the MBE and inducted into the International Rugby Hall of Fame. Beyond his rugby career, he has been involved in broadcasting, charity work, and held positions in various organizations, showcasing his diverse contributions both on and off the field.

Ieuan Wyn Jones, born on May 22, 1949, is a prominent Welsh politician known for his significant contributions to Welsh politics. He served as the Deputy First Minister in the Welsh Government from 2007 to 2011 and was a Member of the National Assembly for Wales for the Ynys Môn constituency from 1999 to 2013. Additionally, Jones held the position of leader of Plaid Cymru from 2000 to 2012. His political career also includes representing the Ynys Môn constituency as a Member of Parliament from 1987 to 2001. Notably, he was named Wales' "Politician of the Year" by the BBC Wales am.pm programme in 2007. Jones' political interests primarily revolve around health and education policy, and he is recognized for his negotiation skills and integrity. Apart from his political endeavors, Jones is a Welsh speaker who has a background in law and is an elder in his local chapel. His personal interests include studying local history, walking, and sports. Jones is also known for his pragmatic approach and ability to navigate between different factions within his party.

Ieuan Rhys, born on December 24, 1961, is a well-known Welsh actor with an extensive career in television and theatre. He is recognized for his role as Seargent Glyn James in the BBC Cymru soap opera "Pobol y Cwm" and as Seargent Tom Swann in the last series of "A Mind to Kill" for Fiction Factory/Channel 5. Rhys also appeared in six series of the Welsh-language version of "Mr and Mrs – Sion a Sian" for HTV, and portrayed Eurig Bell, the Deputy Headmaster in S4C's "Gwaith/Cartref." Rhys received his acting training at The Royal Welsh College of Music & Drama in Cardiff and has appeared in various theatre productions, including works for the National Theatre in London. He has also made notable television appearances in shows like "Doctor Who" and "DaVinci's Demons," showcasing his versatile acting skills. With an impressive career spanning several decades, Ieuan Rhys continues to be a prominent figure in the Welsh entertainment industry.

Ieuan ab Owain Glyndŵr, the reputed illegitimate son of Owain Glyndŵr, the last native-Welsh Prince of Wales, is a historical figure whose existence was uncovered through the work of Peter Bartrum and is currently being edited by the University of Wales Aberystwyth. Information about Ieuan and his descendants can be found in Peniarth Manuscript 287, in the hand of Robert Vaughan of Hengwrt, and in the manuscript known as Harley 1969 by Griffith Hughes. The original manuscripts are kept at the National Library of Wales, Aberystwyth, and the British Library respectively. It is believed that Ieuan was born around 1380 and passed away around 1430. He is thought to have had three sons: Maredudd ab Ieuan ab Owain Glyndŵr, Robert ab Ieuan ab Owain Glyndŵr, and Iorwerth ab Ieuan ab Owain Glyndŵr. These details are sourced from various manuscripts and genealogical works, including those by P. C. Bartrum and the Bartrum Project at the University of Wales, Aberystwyth.

Sir Ieuan Maddock (29 March 1917 – 29 December 1988) was a renowned Welsh scientist and nuclear researcher who made significant contributions to the field of nuclear weapons testing and research. Born in Gorseinon, Glamorganshire, Wales, Maddock graduated from the University of Wales, Swansea with a BSc in physics, later earning a PhD in optical measurements. His career in the civil service saw him play a pivotal role in the British bomb tests of the 1950s and 1960s, and he was instrumental in the development and implementation of the 1973 Partial Test-Ban Treaty, signed by 150 countries. Maddock's influence extended beyond his civil service career, as he continued to serve as an advisor on various committees and held prestigious positions at academic institutions. He was recognized for his contributions with numerous honors and awards, including being elected a Fellow of the Royal Society and appointed a Companions of the Order of the Bath. Maddock's legacy lives on through his extensive publications and his role as a visiting professor at Imperial College London, solidifying his impact on the scientific community.