Erard II, Count of Brienne
Erard II of Brienne( died 1191) was count of Brienne from 1161 to 1191, and a French general during the Third Crusade, most notably at the Siege of Acre.
He was the son of Gautier II, count of Brienne, and Adèle of Baudemont, daughter of Andrew, lord of Baudemont and Agnes of Braine.
His paternal grandparents were Erard I, Count of Brienne and Alix de Roucy.
During this siege he saw his brother André of Brienne die on 4 October 1189, before being killed himself on 8 February 1191.
Erard II's nephew was Erard of Brienne- Ramerupt.
Before 1166 he married Agnès of Montfaucon( † after 1186), daughter of Amadeus II of Montfaucon and of Béatrice of Grandson- Joinville.
Their children were:
Hugh, Count of Brienne
Hugh, Count of Brienne and Lecce( – 9 August 1296) was the second surviving son of Count Walter IV of Brienne and Marie de Lusignan of Cyprus.
John II of Brienne, Count of Eu
John II of Brienne( died 11 July 1302 in Kortrijk) was the son of John I of Brienne, Count of Eu and Beatrice of Saint- Pol.
He succeeded his father as Count of Eu in 1294.
He married Jeanne, Countess of Guînes( d. 1331/ 32), the daughter and heir of Baldwin IV, Count of Guînes.
They had two children: John was killed at the Battle of the Golden Spurs.
John, Count of Brienne
John, Count of Brienne( c. 1235 – c. 1260) was the eldest son of Walter IV of Brienne and Marie of Lusignan, a princess of Cyprus.
He inherited the County of Brienne on his father's death in 1246, but preferred to live among his mother's relatives at the court of Cyprus, and played little part in international politics.
In 1255, he married Marie, Lady of Thieusies( in Hainaut), the daughter of Sohier II of Enghien.
They had no children, and when he died, he was succeeded by his brother Hugh.
Mary of Lusignan, Countess of Brienne
Mary of Lusignan (French: Marie de Lusignan; before March 1215 – 5 July 1251 or 1253), was the wife of Count Walter IV of Brienne and Countess of Brienne from the time of her marriage in 1233 to her husband's death while on Crusade in 1244.
Mary's parents were King Hugh I of Cyprus and Alice of Champagne, making her a maternal granddaughter of Queen Isabella I of Jerusalem.
Her two surviving sons were John, Count of Brienne, and Hugh of Brienne.
Joanna of Châtillon
Joanna of Châtillon or "Joan", ; (c. 1285 – 16 January 1354) was the wife of Walter V of Brienne (1305).
She was Duchess of Athens by marriage (1308–1311).
She was the daughter of Gaucher V de Châtillon, Constable of France and Isabelle de Dreux.
Her paternal grandparents were Gaucher IV de Châtillon and Isabelle de Villehardouin.
Her maternal grandparents were Robert de Dreux, Viscount of Chateaudun and Isabelle de Villebéon.
Erard I, Count of Brienne
Erard I, Count of Brienne( 1060 – 1114) was Count of Brienne at the end of the 11th century.
He was the son of Gautier I of Brienne, count of Brienne, and his wife Eustachie of Tonnerre.
In 1097 he fought in the First Crusade.
In 1110 he married Alix of Roucy- Ramerupt, daughter of André de Montdidier- Roucy, seigneur de Ramerupt.
They had 3 children:
John I of Brienne, Count of Eu
John I of Brienne( died 12 June 1294) was the son of Alphonso of Brienne and Marie de Lusigan.
His mother was the heiress of Eu, Seine- Maritime, and he succeeded his father as Count of Eu in 1270.
He married Beatrice, the daughter of Guy III, Count of Saint- Pol.
They had: John died at Clermont- en- Beauvaisis in 1294.
Ogawa Mataji
Viscount was a general in the early Imperial Japanese Army.
He was also the father- in- law of Field Marshal Gen Sugiyama.
Walter V, Count of Brienne
Walter V of Brienne (– 15 March 1311) was Duke of Athens from 1308 until his death.
Being the only son of Hugh of Brienne and Isabella de la Roche, Walter was the sole heir to large estates in France, the Kingdom of Naples and the Peloponnese.
He was held in custody in the Sicilian castle of Augusta between 1287 and 1296 or 1297 to secure the payment of his father's ransom to the Aragonese admiral, Roger of Lauria.
When his father died fighting against Lauria in 1296, Walter inherited the County of Brienne in France, and the Counties of Lecce and Conversano in southern Italy.
He was released, but he was captured during a Neapolitan invasion of Sicily in 1299.
His second captivity lasted until the Treaty of Caltabellotta in 1302.
Walter settled in France and married Joanna of Châtillon.
After his cousin, Guy II, Duke of Athens, died childless in 1308, Walter laid claim to his inheritance.
Their cousin, Eschiva of Ibelin, also claimed the duchy, but the High Court of Achaea passed a judgement in Walter's favor.
Walter came to Athens in 1309.
John II Doukas, the Greek Lord of Thessaly, made an alliance against him with the Byzantine Empire and the Despotate of Epirus.
Walter hired the Catalan Company, a group of mercenaries, to invade Thessaly.
The Catalans defeated John II, but Walter refused to pay their wages.
After the Catalans rose up in open rebellion, Walter assembled a large army from Frankish Greece, but the Catalans inflicted a crushing defeat on the Franks in the Battle of Halmyros.
Walter died in the battlefield and the Catalans occupied the Duchy of Athens.

Question: Who is Walter V, Count Of Brienne's father-in-law?
Answer: Gaucher V de Châtillon