Ros the Red mac Fergusa Fairrghe, King of Leinster

Ross the Red was an Ulster king. Ross was married to Maga, daughter of Angus Óg. By Maga, Ross was the father of Fachtna, who was his successor. Ross the Red was also married to Roich (Roy) and become mother of Fergus and Sualtam, stepfather of Cu Chulainn.

Maga was later married to Cathbad, the Ard-Druid of Ulaid. Maga had three daughters: Deichtine, Elbha (Elva) and Findchaem (Finchoom). These daughters would later become mothers of heroes who would play important roles in the Ulaid Cycle.

The name House of the Red Branch, originally referred to those who descendants or related to him. Ross the Red's grandson, Conchobar, established a military order of elite warriors as his bodyguards, called the "Red Branch" or Clan Rury, during his reign.

His son Fachtna, succeeded him at his death, married Nessa, and become father of Conchobar, the greatest king of Ulaid (Ulster).