The Green Knight is a recruitable Knight available in place of Sir Tristan or Sir Gawain. During Sir Gawain's quest when you finally discover Lady Isuelet's location and speak with her you have the option to take her to Gawain or let her stay with the Green Knight. if you choose to allow her to stay the Green Knight joins Arthur's Round Table. The Green Knight is a non human/Sidhe Knight making him very unique and starts off as a Old Faith Knight being neither good or evil. The Green Knight wields a huge axe and appears to made in the form of an armoured knight and acts like one too. The Knight is possibly the spirit of the Bedegraine Forest embodied or a druids spirt that became the forests in physical form