Who is Joe Reacher from Killing Floor and what is their importance?

Joe is the first victim in this story. He is introduced as such, having been shot dead, and then savagely kicked repeatedly. Joe was about six foot six inches tall and about two hundred pounds. He was a bald man who had been working as an investigator for the Treasury Department when he was murdered. Hired by Paul Hubble, Joe was meeting with another of Hubble's contacts, Sherman Stoller, when he was killed.