Ó Séaghdha, Diarmaid na Bolgaidhe (c.1755–1846), poet, was born in Dring in the parish of Tuosist, Co. Kerry. Nothing is known of his parents. Local folklore tells that his family descended from a mermaid from whom he inherited his keen intellect and gift for sailing. Numerous other folktales surround his life including three different versions of how he received his ability to compose poetry. He was a seventh son and he was said to have the ability to heal an illness called piast (any illness caused by a worm). The term bolgach (smallpox) in his name refers to the fact that he was marked by smallpox. He was educated in a hedge school in Lochán na gCrann by a poor scholar and is said to have excelled in his class. Although he was able to read, he may never have learned to write, as he never wrote down any of his compositions. He also had a good knowledge of the Bible. According to folklore, he received his gift of poetry one day while sailing between Cork and Cill Macallóg. His biographer, Seán Ó Súilleabháin (qv), considered Ó Séaghdha's laments to be amongst his best compositions and believed that many of his poems had been lost.
A number of stories are told about his dealings with local priests. He is said to have composed the poem ‘An gille mear’ for Fr Aindí Ó Súilleabháin. Indeed, Ó Séaghdha appears to have fallen out with a number of priests, composing satires on them. On one occasion the housekeeper refused him entry to Fr Giolla Ó Súilleabháin's house and in retaliation he cursed both housekeeper and priest. He also composed a satire on the local parish priest in Tuosist entitled ‘Aor an tsagairt’.
He married a woman whose surname was also O'Shea and they lived with his family on a piece of land given to them by his father. He often referred to his wife in his poetry. According to folklore, when the parish priest discovered a number of years later that they were too closely related, he made them separate for a while, even though they were an elderly couple by that stage.
Ó Séaghdha owned his own sailing boat and transported eggs and butter for Tuosist merchants from Cill Macallóg to Cork city, returning with products for them to sell. He also worked on a hooker owned by a Cork merchant. Later in his life he worked as a spailpín or wandering labourer in Waterford. He benefited from the kindness of his friend, the local taoiseach and landlord Mac Fínín Duibh (Sylvester Ó Súilleabháin). Indeed, in one instance, the taoiseach is believed to have saved the poet from being hanged after Ó Séaghdha was wrongly accused of theft. When Mac Fínín Duibh died in 1809, his daughter Lucy announced a competition in which the best lament for her father would receive a prize of ten pounds. Five poets entered the competition, Ó Séaghdha amongst them but he was unsuccessful and it was the weaver, Séamus Ó Caoindealbháin (1775?–1836) from Co. Limerick, who won the prize.
Ó Súilleabháin notes that Ó Séaghdha's compositions after this time are marked by depression and despair. This may be due to the fact that while the taoiseach was alive, Ó Séaghdha did not have to pay rent on his landholding. After Mac Fínín Duibh's death, his brother-in-law became the new landlord and forced Ó Séaghdha to pay rent. He had difficulty raising the money, however, and was often visited by bailiffs. After a gale demolished the roof of his house he was unable to afford its repair and was forced to wander and beg for a living. In 1846 he reached the house of his friend, Aindí Ó Súilleabháin, in Caiseal Coillte, which was by then unoccupied and stayed there until his death later that year. The exact date of his death is unknown but it is believed that he died during the potato famine. Beforehand he sent for Muircheartach Ó Sé, a local man who was able to write, and asked him to write down a poem the poet had composed in the preceding days entitled ‘Aithrighe Dhiarmuda’. This consisted of twenty-one verses and is described by Ó Súilleabháin (1937) as being a fine prayer as well as a fine poem. He died alone either the same night or early the following morning and was dead at least a week before his body was discovered.
A commemorative plaque was erected on 7 July 1930 in Cill Macallóg in his honour and that of poet Mortaí Learaí Ó Súilleabháin.