Henry O'Brien, 5th Earl of Thomond
Henry O'Brien, 5th Earl of Thomond( 1588 – 26 July 1639) was an Irish peer, styled Lord Ibrickane until 1624.
O'Brien was the son of Donogh O'Brien, 4th Earl of Thomond and Elisabeth FitzGerald.
On 13 July 1608 he married Mary Brereton, daughter of William Brereton, 1st Baron Brereton and Margaret Savage, and together they had 5 daughters: O' Brien died in 1639, and was succeeded in his peerages by his brother Barnabas O'Brien, 6th Earl of Thomond.
Henry L. O'Brien
Henry L. O'Brien( c. 1869 – February 8, 1935) was an American politician from New York.
Sir Matthew Dudley, 2nd Baronet
Sir Matthew Dudley, 2nd Baronet (1 October 1661 – 14 April 1721) was an English politician.
Dudley was the son of Sir William Dudley, 1st Baronet, of Clopton, Northamptonshire.
He was the High Sheriff of Northamptonshire for 1684, MP for Northampton from 1703 to 1705 and MP for Huntingdonshire from 1713 to 1715.
He was elected a Fellow of the Royal Society in 1703.
Dudley died in 1721.
he had married Mary, daughter of Henry O'Brien, 7th Earl of Thomond.
He had 4 sons (3 of whom predeceased him) and a daughter.
He was succeeded by his surviving son, Sir William Dudley, 3rd and last Baronet.
Barnabas O'Brien, 6th Earl of Thomond
Barnabas O'Brien, 6th Earl of Thomond (died November 1657), son of Donogh O'Brien, 4th Earl of Thomond; succeeded his brother as earl, 1639; was lord-lieutenant of Clare, 1640–41:
had his rents seized, 1644; admitted a parliamentary garrison to Bunratty Castle and went to England:
joined Charles I; successfully petitioned parliament for £2,000 spent in the parliamentary cause.
Henry O'Brien, 7th Earl of Thomond
Henry O'Brien, 7th Earl of Thomond PC (Ire) (c. 16202 May 1691) was an Irish peer, styled Lord Ibrackan from 1639 to 1657.
O'Brien was the son of Barnabas O'Brien, 6th Earl of Thomond and Anne Fermor.
In 1641, he married his first cousin Anne O'Brien (d. September 1645), daughter of Henry O'Brien, 5th Earl of Thomond, by whom he had one son:
After Anne's death, he married Sarah Russell, daughter of Sir Francis Russell, and widow of Sir John Reynolds.
This made O'Brian a brother-in-law of Henry Cromwell, who had married Sarah's sister Elizabeth.
O'Brian and Sarah had five children:
Henrietta Howard, Countess of Suffolk (died 1715)
Henrietta Howard, Countess of Suffolk( c. 1669 – 10 August 1715), formerly Lady Henrietta Somerset, was the second wife of Henry Howard, 6th Earl of Suffolk.
Lady Henrietta
Somerset was the daughter of Henry Somerset, 1st Duke of Beaufort, and his wife the former Mary Capell.
On 24 June 1686, Lady Henrietta married Henry Horatio O'Brien, son of the Earl of Thomond, who had inherited the courtesy title" Lord Ibrackan" from his elder half- brother in 1678.
They had two children:
Her son Henry inherited the titles of his grandfather, Henry O'Brien, 7th Earl of Thomond.
Lord Ibrackan died of smallpox in 1690.
In April 1705, his widow married Henry Howard, MP, whose wife, Lady Auberie Anne Penelope O' Brien, daughter of the 7th Earl of Thomond( and sister of Henrietta's first husband), had died in November 1703, leaving him with four sons and a daughter.
Henry Howard, then heir to the earldom of Suffolk, was created 1st Earl of Bindon at the end of 1706, making his wife a countess.
He became Earl of Suffolk in 1709.
In 1706, Henry Howard's youngest brother, Charles, married his sister- in- law's namesake, Henrietta Hobart, the ward of Henry and Charles's father, the 5th Earl of Suffolk.
This other Henrietta would become notorious as a royal mistress.
Henrietta and her second husband had no children.
On his death in 1718, he was succeeded in the earldom and in his Lord- Lieutenancy by Charles William, his eldest surviving son from his first marriage.
Henrietta died at Audley End, Essex, and was buried in the Howard family vault at Saffron Walden.
Murrough O'Brien, 1st Earl of Thomond
Murrough O' Brien, 1st Earl of Thomond( died 7 November 1551) was the last King of Thomond, and a descendant of the High King of Ireland, Brian Boru.
Henry Howard, 6th Earl of Suffolk
Henry Howard, 6th Earl of Suffolk, 1st Earl of Bindon PC( 1670 – 19 September 1718) was an English nobleman, styled Lord Walden from 1691 to 1706.
Lord Howard was born in London, the son of Henry Howard, 5th Earl of Suffolk.
He was admitted to Magdalene College, Cambridge, in 1685.
He was returned as Member of Parliament for Arundel in January 1694, but was unseated on petition by John Cooke in February.
He was again returned for Arundel in 1695, holding the seat until 1698.
From 1697 to 1707, he was Commissary- General of the Musters.
In 1705, he was returned for Essex, but left the House of Commons when he was created Earl of Bindon in 1706.
He was the Deputy Earl Marshal in England 1706 – 1718.
In 1708, he was appointed to the Privy Council.
In 1709, he succeeded his father as Earl of Suffolk.
In 1715, he was appointed Lord Lieutenant of Essex and First Lord of Trade, offices he held until his death in 1718.
Howard married his first wife, Lady Auberie Anne Penelope O' Brien, daughter of Henry O'Brien, 7th Earl of Thomond, on 6 September 1691.
She died in November 1703.
They had four sons and one daughter.
In April 1705, he married his second wife, Lady Henrietta Somerset, daughter of Henry Somerset, 1st Duke of Beaufort and widow of Henry Horatio O'Brien, Lord O'Brien.
They had no children.
He was succeeded in the earldom and in his Lord- Lieutenancy by Charles William, his eldest surviving son.
Henry O'Brien, 8th Earl of Thomond
Henry O'Brien, 8th Earl of Thomond( 14 August 1688 – 20 April 1741) was an Irish peer and Member of Parliament.
He was born the son of Henry Horatio O'Brien, Lord Ibrackan, who was to predecease his own father in 1690, allowing the title of Earl of Thomond to pass directly to Henry from his grandfather, Henry O'Brien, 7th Earl of Thomond one year later.
He was elected MP for Arundel, Sussex in the Parliament of the United Kingdom in 1710, sitting until 1714.
He was then ennobled as Viscount Tadcaster.
He served as Governor of County Clare and Governor of Carlow in 1714 and as Lord Lieutenant of Essex from 1721 to 1741.
He died in 1741 and was buried in Limerick Cathedral.
He had married in 1707 Lady Elizabeth Seymour, daughter of Charles Seymour, 6th Duke of Somerset.
They had no children and thus the viscountcy expired.
His other titles were forfeited and were eventually inherited by the earls of Inchiquin.
He left his substantial estates in County Clare to Murrough, Lord O' Brien, the young son of his cousin, William O'Brien, 4th Earl of Inchiquin.
On Murrough's death in 1741, the estates passed instead to Percy Wyndham, a nephew of Henry's wife, who took the additional surname of O'Brien and in 1756 was created Earl of Thomond.
Henry O'Brien, Lord Ibrackan
Henry O'Brien, Lord Ibrackan, or Lord O'Brien( c. 1642 – 1 September 1678), styled Hon. Henry O'Brien until 1657, was an Irish nobleman and politician.
He was the son of Henry O'Brien, 7th Earl of Thomond, and his first wife, and cousin, Anne O'Brien.
He married Katherine Stuart, 7th Baroness Cifton, daughter of George Stuart, 9th Seigneur d'Aubigny and Lady Katherine Howard: the Aubigny Stuarts were a junior branch of the reigning House of Stuart.
They had six children( of whom three died young):
In 1661, he represented Clare in the Parliament of Ireland, and from 1670 until his death in 1678, Northampton.
In 1673, he was appointed to the Privy Council of Ireland.
His wife's relationship to Charles II gave them a valuable opening at Court, where they already had a friend in Sir Joseph Williamson and they enjoyed high favour in the 1660s.
He died of disease while in camp with his regiment in Flanders.
His courtesy title passed to his younger half- brother Henry Horatio O'Brien, Lord Ibrackan.
Katherine within three months married their old friend, the statesman Sir Joseph Williamson.
The speed of her remarriage gave rise to unkind rumours that the pair had been lovers, and the marriage was disapproved of, even by her children, since Williamson, the son of a country vicar, was not considered a suitable match for a connection of the King.
He is a major character in" The Piccadilly Plot", the seventh in the Thomas Chaloner mystery novels by Susanna Gregory.

Question: Who is Henry O'Brien, 7Th Earl Of Thomond's paternal grandfather?
Answer: Donogh O'Brien, 4th Earl of Thomond