Guitier (Ithier) of Rethel (died 1171), son of Odo, Castellan of Vitry and Matilda, Countess of Rethel, nephew of Baldwin II of Jerusalem, was count of Rethel, succeeding his mother. In March 1129, Guitier travelled to the Holy Land, although it is not clear if he participated in the Damascus Crusade that year.
Guitier married Beatrice, daughter of Count Godfrey I of Namur and Erminside of Luxembourg. Guitier and Beatrix had eleven children:
Beatrice (1130 – 30 March 1185), married King Roger II of Sicily
John (died after 1144)
Manasses (died after 1144)
Hugh(died after 1166), a monk at Reims
Manasses IV (died 1199)
Henry (died 1191), castellan of Vitry
Baldwin (died 1198 or after), lord Chemery
Albert (died 1195 or after), archdeacon at Liège
Simon
Clemence (died after 1190), married Hugh of Pierrepont
Daughter (name unknown), married Geoffroy, Vidame de Châlons.
Upon his death, he was succeeded as count of Rethel by his son Manasses IV.