A knight of the Templar Order, he is Ivanhoe's archetypal nemesis. He joined the Templars, a powerful international militaristic/religious organization, not for spiritual idealism but because he was betrayed by the woman he loved. He went to the Crusades where, like Ivanhoe, he gained fame for his bravery and courage. He is a weak moralist consumed by ambition and often lets his temptations take control of him. He allied himself with Prince John, the greedy brother of King Richard. He falls in love with Rebecca and kidnaps her. Although she does not return his affections, she brings out his more admirable qualities.
He appears as a tall muscular man, past forty, with darkly tanned skin from constant sun exposure while in the Holy Land. He has great skill with the sword and, like Ivanhoe, knows several exotic languages. Unlike Ivanhoe, he is prone to prejudices, which are common during the times. He tends to look down on Saxons and other cultures not equal to his Norman upbringing.
There are tons of possibilities for introducing Bois-Guilbert into a Robin Hood Campaign. The PCs could be looking for a lost religious relic only to find out that Bois-Guilbert and his Templar-Knights have taken it. Or Bois-Guilbert has hatched up a plot with Prince John to get rid of Robin Hood and his gang of Merry Men, and it is up to the PCs to warn Robin and stop Bois-Guilbert from succeeding.