Egas was the eldest son of Moninho Viegas, o Gasco,[1] who is generally considered the founder of the House of Ribadouro.
Old accounts tell that in 999, in a year of change in the kingdom of León, when Bermudo II died and Count Mendo Gonçalves of Portugal became regent of the young Afonso V of León, a landing of Christians took place at the mouth of the Douro, commanded by Monio Viegas, the supposed founder of the Ribaduriense (or Gascan) lineage, who was said to have originated in Gascony.
[2] This information may be credible, but in a donation that Garcia Moniz made in 1068 to the King of Galicia, it refers to goods that he had inherited from his grandparents, so that these, the supposed parents of the “founder from Gascony” already had control in Ribadouro, and so Monio did not conquer such control, but inherited it, and therefore could not come from Gascony, as he was a native of Portugal, probably from a Portuguese place called Gasconha (or Casconha in the current municipality of Paredes).
[1] Egas inherited several assets in Ribadouro from his father, especially in the regions of Penafiel (Galegos, Canelas, etc.)
[1] He married Toda Ermiges da Maia, who, in addition to being a first cousin of the first lord of Maia, Trastamiro Aboazar, was the maternal granddaughter of Trutesendo Galindes, from the influential lineage of the founders of Paço de Sousa Monastery.