Greg (Season 3)

Greg is a friend of Rick.

History
Greg, Rick, and Vince were on the ferry that was in a crash. They helped many other people get out before Rick was trapped between two cars. Vince left to get help and brought back Izzie Stevens. Vince and Greg helped her treat Rick as best she could. Greg was then sent to get Search and Rescue to get Rick out, but he came back alone, saying that Search and Rescue had many emergent patients that needed help. ("Walk on Water")

Friendships
He, Vince, and Rick are all good friends.