Question: Who is Margaretta Foster, 1St Viscountess Ferrard's paternal grandfather?

Knowledge 1: Margaretta Foster, 1st Viscountess Ferrard
Margaretta Amelia Foster, 1st Viscountess Ferrard ("née" Burgh; c. 1737 – 20 January 1824) was an Anglo-Irish peeress.She was the daughter of Thomas Burgh and Anne Downes, daughter of Dive Downes, Bishop of Cork and Ross and his fourth wife Lady Catherine Fitzgerald.On 14 December 1764, she married the politician John Foster.On 5 June 1790, she was raised to the Peerage of Ireland as Baroness Oriel in her own right.The title was created in honour of her husband, but in such a way that would enable him to continue to serve as Speaker of the Irish House of Commons.On 22 November 1797, she was further honoured when she was made Viscountess Ferrard.Her husband was created Baron Oriel in his own right in 1821.Viscountess Ferrard had three children.She was succeeded in her titles by her eldest surviving son by John Foster, Thomas, who also succeeded to his father's barony on his death in 1828. [SEP] Knowledge 2: Thomas Burgh (Lanesborough MP)
Thomas Burgh (1696 – 20 September 1758) was an Anglo-Irish politician.He was the son of William Burgh and Margaret Parnell.Burgh sat in the Irish House of Commons as the Member of Parliament for Lanesborough between 1727 and his death in 1758.Burgh married Anne Downes, daughter of Rt.Rev. Dive Downes, Bishop of Cork and Ross and his fourth wife Lady Catherine Fitzgerald, sister of the Earl of Kildare, in 1731.They had eight children, three sons and five daughters.One of their daughters, Margaretta Burgh, married John Foster, 1st Baron Oriel and was created Viscountess Ferrard in 1797.One of his sons, also called Thomas, was the father of Ulysses Burgh, 2nd Baron Downes, who inherited the title by special remainder from his cousin William Downes, 1st Baron Downes, Lord Chief Justice of Ireland, a nephew of Anne Downes.
Knowledge 1: Margaretta Foster, 1st Viscountess Ferrard
Margaretta Amelia Foster, 1st Viscountess Ferrard ("née" Burgh; c. 1737 – 20 January 1824) was an Anglo-Irish peeress.She was the daughter of Thomas Burgh and Anne Downes, daughter of Dive Downes, Bishop of Cork and Ross and his fourth wife Lady Catherine Fitzgerald.On 14 December 1764, she married the politician John Foster.On 5 June 1790, she was raised to the Peerage of Ireland as Baroness Oriel in her own right.The title was created in honour of her husband, but in such a way that would enable him to continue to serve as Speaker of the Irish House of Commons.On 22 November 1797, she was further honoured when she was made Viscountess Ferrard.Her husband was created Baron Oriel in his own right in 1821.Viscountess Ferrard had three children.She was succeeded in her titles by her eldest surviving son by John Foster, Thomas, who also succeeded to his father's barony on his death in 1828. [SEP] Knowledge 2: John Foster, 1st Baron Oriel
John Foster, 1st Baron Oriel( 1740 – 23 August 1828) was an Irish peer and politician, who served as Chancellor of the Exchequer of Ireland and as the last Speaker of the Irish House of Commons.
Knowledge 1: Margaretta Foster, 1st Viscountess Ferrard
Margaretta Amelia Foster, 1st Viscountess Ferrard ("née" Burgh; c. 1737 – 20 January 1824) was an Anglo-Irish peeress.She was the daughter of Thomas Burgh and Anne Downes, daughter of Dive Downes, Bishop of Cork and Ross and his fourth wife Lady Catherine Fitzgerald.On 14 December 1764, she married the politician John Foster.On 5 June 1790, she was raised to the Peerage of Ireland as Baroness Oriel in her own right.The title was created in honour of her husband, but in such a way that would enable him to continue to serve as Speaker of the Irish House of Commons.On 22 November 1797, she was further honoured when she was made Viscountess Ferrard.Her husband was created Baron Oriel in his own right in 1821.Viscountess Ferrard had three children.She was succeeded in her titles by her eldest surviving son by John Foster, Thomas, who also succeeded to his father's barony on his death in 1828. [SEP] Knowledge 2: Dive Downes
Dive Downes( b Thornby, Northamptonshire 1652 – d Dublin 1709) was Bishop of Cork and Ross from 1699 to 1709.Downes was born in Northamptonshire, son of the Reverend Lewis Downes.He was educated at Trinity College, Dublin.He was ordained in 1678.In 1683 he became a prebendary of St Patrick's Cathedral, Dublin and in 1690 Archdeacon of Dublin.He was married four times.He married firstly Sarah Dodwell, dughter of Henry Dodwell of Athlone, secondly Anne Carleton, and thirdly Elizabeth Beecher, daughter of Thomas Beecher of Sherkin and widow of Horatio Townshend, by whom he had a daughter Elizabeth, who married her cousin Henry Baldwin of Mount Pleasant.By his fourth wife Catherine FitzGerald, daughter of the Honorable Robert FitzGerald and Mary Clotworthy, and sister of Robert FitzGerald, 19th Earl of Kildare, he had a son Robert Downes, MP for Kildare, of Donnybrook Castle, and a daughter Anne.Robert was the father of William Downes, 1st Baron Downes, Lord Chief Justice of Ireland.Anne married Thomas Burgh and was the mother of Margaretta Foster, 1st Viscountess Ferrard, and grandmother of Ulysses Burgh, 2nd Baron Downes.He was a conscientious bishop, and in 1699- 1700 he visited every parish in his diocese: his" Visitation of Cork" has survived.

Answer: William Burgh