Mac Coitir, Uilliam (Liam) ‘Rua’ (c.1675–1738), poet, was born at Curraghdermot, near Castlelyons, Co. Cork. Nothing is known of his parents except that his mother was a Murphy, but he had at least two brothers, Éamonn and Séamas. The latter, known as Séamas Mór Mac Coitir, was the father of Séamas Beag Mac Coitir, and both father and son were themselves poets. As Mac Coitir remained in his native district throughout his life and does not appear to have married, it has been conjectured that he may have resided with his brother, Séamas, and the latter's family. He was a tailor by trade and in his youth he excelled as an athlete and hurler.
East Cork was an important centre of literary and scribal activity during Mac Coitir's lifetime, and the poets with whom he associated included Fr Conchobhar Ó Briain, parish priest of Castlelyons; Liam Inglis (qv), who spent some time in the same locality; Éamonn de Bhál (qv) from Dungourney; Seán na Ráithíneach Ó Murchadha (qv) and Liam Mac an Dúna Cairteáin (qv), both from Carrignavar; and Eoghan an Mhéirín Mac Cárthaigh (qv), from Aherla, to the west of Cork city. These poets, and other lesser figures, were loosely associated in what is often termed the Blarney court of poetry. This took the form of a series of irregular gatherings at which the poets of the region assembled in a convivial atmosphere to hear and to discuss each other's compositions. A poem (‘Tabhair mo pháirt chaoin fá thrí’) addressed to Mac Coitir by Seán Smíst in 1720 indicates that he had already acquired a reputation as a poet among his peers, but the earliest of his extant works that can be positively dated were all written after that year. These include his longest and best-known work, a lament (‘Mór an chreill seo gheibhim do chéas mé’) of more than 300 lines for James Cotter (qv), a prominent Jacobite and a catholic member of the east Cork gentry who was hanged in 1720 having been convicted of rape in what was widely regarded as a politically inspired trial. This was the view taken by Mac Coitir, who referred in his lament to ‘an t-óg nár mheata gur teascadh le héiteach’ (‘the uncowardly young man cut down by perjury’). In 1724 Mac Coitir composed an elegy (‘Cé is urra don iaith seo Bhriain’) on the death of Uilliam Mac Cairteáin an Dúna, and he subsequently came to be regarded as Mac Cairteáin's successor as presiding officer of the Blarney court of poetry. Other notable works by Mac Coitir include a poem (‘An suairc libh an gáir-ghol so ag Sámuel is ag Seón?’) that celebrated the outbreak of hostilities between Britain and Spain and looked forward to a Spanish victory – a composition that may be associated with the war of 1718–20 or, what may be more likely in view of a reference to Gibraltar, with the brief undeclared war of 1727; an undatable Jacobite song (‘Is briathra leamha ar ollbhaois’), in which Ireland is portrayed in the guise of Móirín Ní Luinneacháin; a religious work (‘Na bearta san do chleachtainnse’), in which the poet confesses his sins and seeks the Virgin Mary's intercession on his behalf; and a somewhat anti-clerical piece (‘A chliar ná molann an t-ól’) which contrasts clerical strictures on the consumption of alcohol with the clergy's own non-abstemious behaviour.
Mac Coitir died 12 July 1738 and was buried in Britway churchyard, about three miles from Castlelyons. His death was lamented in elegies by Séamas Beag Mac Coitir, Éamonn de Bhál, and Seán Ó Murchadha na Ráithíneach.