Not to be confused with Mack, the core team member
Agent Mack was an employee of the Strategic Homeland Intervention Enforcement and Logistics Division.
In October of 2013, he went undercover (as a longhaul trucker for 'Rocky Mountain Office Supplies'), driving a S.H.I.E.L.D. Freightliner that was covertly transporting scientist Franklin Hall. The convoy was attacked in Colorado, but Mack survived the encounter intact, and was able to give the team an eyewitness account.