Quote from : The Fellowship of the Ring Book

For the rest, they shall represent the other Free Peoples of the World: Elves, Dwarves, and Men, Legolas shall be for the Elves; and Gimli son of Gloin for the Dwarves. They are willing to go at least to the passes of the Mountains, and maybe beyond. For Men you shall have Aragorn son of Arathorn, for the Ring of Isildur concerns him closely