Friday is the first person Crusoe introduces into the social order of the island. His name, of course, isn't Friday by birth, but this is the name that Crusoe gives him after saving him from the hands of the cannibals. Crusoe also teaches Friday to speak English, encourages him to eat goat (you know, instead of human flesh), and aids in his conversion to Christianity.
The first and most obvious point about Friday's relationship with Crusoe is that Friday is Crusoe's subordinate. Friday always calls Crusoe "master," for example. Crusoe also mentions that their relationship is much like that of "a Child to a Father" (176). Why does Crusoe not see Friday as his equal, even after Friday converts to Christianity?
Crusoe's dominant relationship to Friday produces a pretty interesting dynamic between the two of them. See, for example, Crusoe's description of Friday as he is sleeping:
He was a comely handsome Fellow, perfectly well made; with straight strong Limbs, not too large; tall and well shap'd, and as I reckon, about twenty six Years of Age. He had a very good Countenance, not a fierce and surly Aspect; but seem'd to have something very manly in his Face, and yet he had all the Sweetness and Softness of an European in his Countenance too, especially when he smil'd. His Hair was long and black, not curl'd like Wool; his Forehaed very high, and large, and a great Vivacity and sparkling Sharpness in his Eyes. The Coulour of his Skin was not quite black, but very tawny; and yet not of an ugly yellow nauseous tawny, as the Brasilians, and Virginias, and other Natives of America are; but of bright kind of a dun olive Colour, that had in it something very agreeable; tho' not very easy to describe. (173)
Crusoe spends a great deal of time describing Friday's body, to be sure, especially the ways in which he resembles a European.