This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Fir Bolg (Irish)
In medieval Irish myth, the Fir Bolg (also spelt Firbolg and Fir Bholg) are the fourth group of people to settle in Ireland. They are descended from the Muintir Nemid, an earlier group who abandoned Ireland and went to different parts of Europe. Those who went to Greece became the Fir Bolg and eventually return to Ireland, after it had been uninhabited for many years. After ruling it for some time and dividing the island into provinces, they are overthrown by the invading Tuatha Dé Danann.
Lebor Gabala Frenn tells of Ireland being settled six times by six groups of people. The first three—the people of Cessair, the people of Partholón, and the people of Nemed—were wiped out or forced to abandon the island. The Fir Bolg are said to be descendants of the people of Nemed, who inhabited Ireland before them. Those who went to Greece became the Fir Bolg where they were enslaved by the Greeks and made to carry bags of soil or clay, hence the name 'Fir Bolg' (men of bags)