In Scotland a race of giants; in Ireland a race of evil demons. In both countries they were the original occupants of the land, who had to be subdued by any invaders.
The Partholons, who were the first to invade Ireland, fought many bloody battles against the Fomorians but could not defeat them, and eventually died in a kind of biological warfare when the Fomorians afflicted them all with plauge. They were followed by the Nemeds, who lost their very first battle against the demons. The Fomorians enslaved them and forced them to pay an annual tribute of cattle and children.
Successive waves of invaders included the Fir Bolga, who managed to subdue the Fomorians and live peacefully with them on the island. When the Tuatha conquered the Fir Bolga, they dealt more subtly with the Fomorians. They made friends with them and even married some of the demons, but when the Femorians allowed themselves to relax the Tuatha set upon them and slaughtered the entire community.
The Fomorians of Scotland were a less warlike race than those of Ireland. Despite their giant stature they offered little resistance to invasion and gradually allowed themselves to be absorbed by their conquerors, which may be the reason for the size and strength of many Scotsmen of the present day.