Geoffrey Ier OF CHÂTEAUDUN , Vicomte de Châteaudun

  General Notes:

https://en.wikipedia.org/wiki/Geoffrey_I,_Viscount_of_Ch%C3%A2teaudun
Geoffrey I (Gauzfred I) (d. after 985), Viscount of Châteaudun, possibly the son of Geoffroy, Viscount of Chartres. Geoffrey was appointed viscount by Theobald the Trickster, in his position of Count of Châteaudun. Geoffrey was the founder of the House of Châteaudun, which gave rise to both the House of Ingelger and House of Plantagenets. It is believed, but unverified, that Geoffrey descended from Rogron I, Count of Maine, and therefore part of the Rogonid/Rorgonid dynasty. Little is known about Geoffrey, other than he was closely associated with Hardouin, Archbishop of Tours.

Geoffrey married Ermengarde of an unknown family and had one child:

Hugues, Viscount of Châteaudun
Geoffrey was succeeded by his son as Viscount of Châteaudun upon his death. There are differing accounts about Geoffrey and his offspring. One prominent theory is that Geoffrey and Hughes were the same person, and that Ermengarde was Geoffrey's first wife, and Hildegard, the wife of Hughes, was his second.

Geoffrey married Ermengarde.