The term goblins actually comprises three separate subspecies of creatures. It also refers specifically to the smallest and most numerous subspecies of these three.
Proper goblins are small, even more so than halflings. They breed very quickly and are known for a voracious appetite for food, land, treasure, and anything else they can get their hands on. Their skin tone tends to be yellow to reddish.
Hobgoblins are larger and more militaristic. They tend to have redder or more orangey skin. They tend to be leaders and organizers of their race, more apt to work together and to get other goblins to band together for a common goal.
Bugbears are the largest of the subspecies,with yellow-brownish skin and thick fur which grows on them, including mane-like hair. They tend to be solitary bullies, except when rallied by hobgoblins to be champions and elite shock troops.
Goblins are believed to be native to Aldorath, and they once claimed much of the northeastern and eastern lands for their own. Their lands had diminshed by the time of the First Conclave of the Seven Kingdoms, both from human and orcish encroachment. They joined the alliance as the kingdom of Gristamere, and they reluctantly accepted that the Northmen and Summerlings had a right to lands they themselves had once occupied. It may be resentment from these times that ultimately led to them joining forces with the Witch Queen.