Máire Rua O'Brien (1615/1616 – 1686) was an Irish aristocrat who married three times to retain family lands. Born into the MacMahon family of Thomond, her name, Máire Rua or Red Mary, derived from her red hair. First married to Daniel Neylon (O'Neillan) of Dysert O'Dea Castle in north County Clare, after his death in 1639, she married Conor O'Brien of Leamaneh Castle. With her second husband, she backed the Confederate cause against Cromwell's forces during the Eleven Years' War. However, after her second husband was killed in 1651, she married a Cromwellian officer; in a reputed attempt to save her estate. Remaining on her estate at Leamaneh for several decades, her son Donough O'Brien moved the family seat to the larger Dromoland Castle where she lived until her death in 1686. A sometimes notorious figure in Irish folklore, a number of exaggerated stories and legends are associated with her life.