I was searching around at enclyclopedia Mythica and found this article on Formorians:
In Irish-Celtic mythology, the Fomorians are a race of demonic giants, ancient occupants of Ireland (or sometimes mentioned as a mythical, prehistoric people who raided and pillaged Ireland from the sea). The first to invade Ireland were the Partholons, but after many battles the Fomorians afflicted them all with plague. After them came the Nemeds, who in their very first battle were defeated and enslaved. The third wave of invaders, the Firbolgs, were more successful and they subdued the Fomorians and managed to live peacefully with them.
After a period of peace, the Tuatha Dé Danann, the Irish race of gods, arrived. They conquered the Firbolgs, but dealt more subtly with the Fomorians, although they destroyed their hegemony over Ireland for good in the second battle of Mag Tuireadh. The Fomorians were given the province of Connacht, and were even allowed to marry some of the Tuatha Dé. The king of the Fomorians is the one-eyed Balor. Other prominent members are: Bres, Eriu, and Tethra.
The Fomorians are sometimes mythologically associated with the powers of nature which challenge man: fog, storm, winter, disease, crop-blight. The name comes from fomó, "giant", "pirate".
Related information
Other names
Fomors
I also found some stuff on trow and thrall. It seems that bungie took a liking to Irish and Norse Mythology a whole deal.
