Question: Who is Maurice De Berkeley, 4Th Baron Berkeley's maternal grandfather?

Knowledge 1: Maurice de Berkeley, 4th Baron Berkeley
Maurice de Berkeley, 4th Baron Berkeley (c. 1330 – 8 June 1368), "The Valiant", feudal baron of Berkeley, of Berkeley Castle in Gloucestershire, was an English peer.His epithet, and that of each previous and subsequent head of his family, was coined by John Smyth of Nibley (died 1641), steward of the Berkeley estates, the biographer of the family and author of "Lives of the Berkeleys".He was born in Berkeley Castle in Gloucestershire, the eldest son and heir of Thomas de Berkeley, 3rd Baron Berkeley by his wife Lady Margaret Mortimer.In August 1338 Berkeley married Elizabeth le Despenser, daughter of Hugh Despenser the younger by his wife Eleanor de Clare.By Elizabeth he had seven children as follows: [SEP] Knowledge 2: Margaret Mortimer, Baroness Berkeley
Margaret Mortimer, Baroness Berkeley (2 May 1304 – 5 May 1337) was the wife of Thomas de Berkeley, 3rd Baron Berkeley.She was the eldest daughter of Roger Mortimer, 1st Earl of March, the "de facto" ruler of England from 1327 to 1330, and his wife Joan de Geneville, Baroness Geneville.
Knowledge 1: Margaret Mortimer, Baroness Berkeley
Margaret Mortimer, Baroness Berkeley (2 May 1304 – 5 May 1337) was the wife of Thomas de Berkeley, 3rd Baron Berkeley.She was the eldest daughter of Roger Mortimer, 1st Earl of March, the "de facto" ruler of England from 1327 to 1330, and his wife Joan de Geneville, Baroness Geneville. [SEP] Knowledge 2: Thomas Berkeley, 5th Baron Berkeley
Thomas Berkeley, "de jure" 5th Baron Berkeley, (b. 1472 - 22 January 1532) was a British soldier and aristocrat.He was born to Sir Maurice Berkeley, "de jure" 3rd Baron Berkeley, and Isabel Meade, in England.He was the younger brother to Maurice Berkeley, "de jure" 4th Baron Berkeley, and had a younger brother, James, and younger sister, Anne.On 9 September 1513 he fought in the Battle of Flodden and was knighted by the Earl of Surrey, Thomas Howard.He later became Constable of Berkeley Castle on 15 May 1514, and Sheriff of Gloucestershire, November 1522 - November 1523.By writ, he was succeeded to the title of "de jure" 5th Baron Berkeley on 12 September 1523 after his brother Maurice's death, and his eldest son Thomas followed as the "de jure" 6th Baron Berkeley, again by writ.
Knowledge 1: Maurice de Berkeley, 4th Baron Berkeley
Maurice de Berkeley, 4th Baron Berkeley (c. 1330 – 8 June 1368), "The Valiant", feudal baron of Berkeley, of Berkeley Castle in Gloucestershire, was an English peer.His epithet, and that of each previous and subsequent head of his family, was coined by John Smyth of Nibley (died 1641), steward of the Berkeley estates, the biographer of the family and author of "Lives of the Berkeleys".He was born in Berkeley Castle in Gloucestershire, the eldest son and heir of Thomas de Berkeley, 3rd Baron Berkeley by his wife Lady Margaret Mortimer.In August 1338 Berkeley married Elizabeth le Despenser, daughter of Hugh Despenser the younger by his wife Eleanor de Clare.By Elizabeth he had seven children as follows: [SEP] Knowledge 2: Thomas Berkeley, 5th Baron Berkeley
Thomas Berkeley, "de jure" 5th Baron Berkeley, (b. 1472 - 22 January 1532) was a British soldier and aristocrat.He was born to Sir Maurice Berkeley, "de jure" 3rd Baron Berkeley, and Isabel Meade, in England.He was the younger brother to Maurice Berkeley, "de jure" 4th Baron Berkeley, and had a younger brother, James, and younger sister, Anne.On 9 September 1513 he fought in the Battle of Flodden and was knighted by the Earl of Surrey, Thomas Howard.He later became Constable of Berkeley Castle on 15 May 1514, and Sheriff of Gloucestershire, November 1522 - November 1523.By writ, he was succeeded to the title of "de jure" 5th Baron Berkeley on 12 September 1523 after his brother Maurice's death, and his eldest son Thomas followed as the "de jure" 6th Baron Berkeley, again by writ.

Answer: Roger Mortimer, 1st Earl of March