Cathbad, also spelled Cathbhadh,  in the Irish sagas, the great Druid of Ulster and, in some legends, the father of King Conchobar mac Nessa (Conor).

Cathbad was able to divine the signs of the days, thus to determine auspicious or inauspicious activities for certain days. According to one tradition, the queen Nessa once consulted Cathbad, asking him what the day was auspicious for; Cathbad answered that it was auspicious for begetting a king upon a queen, and Conchobar was conceived in their subsequent union. When Conchobar reached manhood, none in Ulster was allowed to speak before he had spoken, but Conchobar never spoke before Cathbad had spoken—giving Cathbad precedence over the king. Cathbad acted as the king’s advisor and is referred to as a teacher, supporting Julius Caesar’s assertion that the Gallic Druids served as repositories of traditional knowledge.