In LOTR the orcs are the elves, and also orc is another word for goblin. In mythology, dwarves are a subspecies of elves, and so are many other creatures. Hobbits were based on domestic spirits like brownies, which were also subspecies of elves as well. Also, trolls, ogres, and giants were pretty interchangeable as well. The ents came from creatures like the green men, and the name of the ents came from the name of the giants. A lot of inspiration for LOTR came from a combination of celtic and germanic mythology from their indigenous pagan (pre-abrahamic, polytheistic, animistic religions), mixed heavily with British Catholic Christianity in a sort of syncreticism of the fictional worlds. Pretty much everything but the names and made up languages were entirely ripped off from concepts found in the public domain of the time.