Greg Jennings is the brother of Samantha Jennings.
Greg first appears in The Recruit, when he attacks James Adams, he grazes James' face across a brick wall, punches him in the gut and steals James' money. This was as revenge for James's attack on his sister.
He is seen again later on in the book, when James returns with Bruce, Kyle and Lauren. During the fight, both of Greg's thugs are rendered unconscious. Greg pulls out a knife but is disarmed by Bruce. Greg then flees the fight.