Not much is known of his background other than the fact that he's a criminal and never made it past the sixth grade. As for weapons, he has a crow bar (like Marv) which he uses to break into Kevin's house and a gun which becomes useless when it's filled with a sort of slime from Kevin's booby traps. So, he never uses it and it's supposedly taken away by the police. In the second film, Harry still has the "M" from the McCallister doorknob branded on his hand from when he touched it not knowing that Kevin had heated it up.