In the excerpt from Sir Gawain and the Green Knight, the Green Knight is a typical medieval romance character because he

..... is a magical being.

The Green Knight is a typical medieval character because he undertakes a quest.

According to M. H. Abrams, it's standard plot is that of a quest undertaken by a single Knight in order to gain a lady's favour, frequently it's central interest is courtly love, together with tournaments fought and dragons and monsters slain for the damsel's sake, it stresses the chivalric ideals of courage, loyalty, honour, mercifulness to an opponent and elaborate manners, and it delights in wonders and marvels.