There are two people named Agnoman in The Book of Invasions, both originally from Scythia:

Agnoman, father of Nemed

The first Agnoman was the father of Nemed, the third invader of Ireland. His father was Piamp, and his grandfather was Tait, a brother of Partholon.

Agnoman, father of Lamfhind

The second Agnoman was the father of Lamfhind, and therefore, one of the Gaels. Agnoman was forced to leave Scythia when he killed Refloir, the king, for unknown reasons. Agnoman died on the Caspain Sea, thus making Lamfhind the leader of the Gaels.