Individual Details

Geoffrey was Earl of Essex in right of his first wife. Justiciar of England 1198-1213. He was the son of Piers de Lutegareshale who died by 1198 and Maud de Mandeville, Lady of Costow, County Wilts.

Wikipedia:
Geoffrey Fitz Peter, Earl of Essex (c. 1162–1213) was a prominent member of the government of England during the reigns of Richard I and John. The patronymic is sometimes rendered Fitz Piers, for he was the son of Piers de Lutegareshale, forester of Ludgershall.
He was from a modest landowning family that had a tradition of service in mid-ranking posts under Henry II. Geoffrey's elder brother Simon of Pattishall was at various times High Sheriff of Northamptonshire, Essex, and Hertfordshire. Geoffrey, too, got his start in this way, as High Sheriff of Northamptonshire for the last five years of Henry II's reign.
Around this time Geoffrey married Beatrice de Say, daughter and eventual co-heiress of William de Say II. This William was the son of William de Say I and Beatrice, sister of Geoffrey de Mandeville, 1st Earl of Essex. This connection with the Mandeville family was later to prove unexpectedly important. In 1184 Geoffrey's father-in-law died, and he received a share of the de Say inheritance by right of his wife, co-heiress to her father. He also eventually gained the title of earl of Essex by right of his wife, becoming the 4th earl.

When Richard I left on crusade, he appointed Geoffrey one of the five judges of the king's court, and thus a principal advisor to Hugh de Puiset, Bishop of Durham, who, as Chief Justiciar, was one of the regents during the king's absence. Late in 1189, Geoffrey's wife's cousin William de Mandeville, 3rd Earl of Essex died, leaving no direct heirs. His wife's inheritance was disputed between Geoffrey and his in-laws, but Geoffrey used his political influence to eventually obtain the Mandeville lands (but not the earldom, which was left open) for himself.
He served as High Sheriff of Yorkshire from 1198 to 1201 and again in 1203 and as High Sheriff of Bedfordshire and Buckinghamshire from 1200 to 1205 [1]. On 11 July 1198, King Richard appointed Geoffrey Chief Justiciar, which at that time effectively made him the king's principal minister. He continued in this capacity after the accession of king John until his death on 14 October 1213.[2] On his coronation day the new king ennobled Geoffrey as Earl of Essex.

Spouses
m1. Beatrice de Say, daughter of William de Say.[3]
m2. Aveline, daughter of Roger de Clare, 2nd Earl of Hertford.

Children of Beatrice
Note that his sons by this marriage took the de Mandeville surname.
Geoffrey FitzGeoffrey de Mandeville, 2nd Earl of Essex.
William FitzGeoffrey de Mandeville, 3rd Earl of Essex.
Henry, Dean of Wolverhampton.
Maud Fitzgeoffrey, who married Henry de Bohun, 1st Earl of Hereford.

[edit] Children of Aveline
John Fitzgeoffrey, Lord of Shere and Justiciar of Ireland.
Cecily Fitzgeoffrey.
Hawise Fitzgeoffrey.

Geoffrey's first two sons died without issue. Apparently the earldom was associated with their mother's Mandeville heritage, for the earldom was inherited by Henry De Bohun, the husband of their sister Maud, instead of their half-brother John.

Birth	1162
Marriage	Bef 29 May 1205	Aveline de Clare
Death	14 Oct 1213	Essex, England
Burial		Shouldam Priory, Norfolk, England

Spouse	Aveline de Clare ( - 1225)
Child	Hawise Fitz Geoffrey ( - 1243)
Child	Sir John Fitz Geoffrey Lord of Shere, Justiciar of Ireland (1208 - 1258)