Mack Gruber is a private contractor. A handy man of sorts. Problem is he isn't all that handy. He's the guy you hire when you cannot afford to get the job done right and you’ll probably be left worse off than before you called.
A while back Gruber came to Chernarus to visit his brother, who lives in Dobroe. That's when everything went sideways.
Huddled in the woods surrounding Dabroe, its amazing that Gruber is still alive. He was never able to find his brother but still holds out hope he's alive. Depending on his handy man skills to survive, he is willing to take on any contract offered to him, but never guarantees he'll get the job done.