In the book Robinson Crusoe (and to a lesser extent the movie Robin Hood: Prince of Thieves), there is a character who, when his life is saved by the protagonist, swears allegiance (and, basically, servitude) until death or the favor is returned. It is implied that this is something which is a part of the culture of the person who's life is saved.
While I am aware that such things are possible, they most certainly were not a part of Native American culture, but I was curious if any such culture exists or existed past?