The Knight travels with only one servant, or yeoman, and one who looks like Robin Hood. Seriously, this guy is dressed all in green and decked out with a bow and arrows, a dagger, and a sword. His hair is short, and his face is brown, suggesting that he spends a lot of time outside. Chaucer tells us he's a forester – at home he probably takes care of the forests on the Knight's land, protecting them from outlaws and making sure nobody poaches in them. As foresters go, he's probably a good one, a conclusion we can draw because he keeps his bow and arrows in very good condition – no droopy feathers for him – so it's likely he keeps his forest in similarly tip-top shape.
We never see the Yeoman again after the General Prologue, but, from him, we learn two things about the Knight: 1) that he's not high-maintenance, because he travels with only one servant, and 2) that he owns some land – hence, his need for a forester.