Who is Mr. Mantz from Factotum and what is their importance?

Mr. Mantz owns the warehouse where he Henry Chinaski is hired. When Mantz notices Henry doing less and less, he fires him. Henry lashes out: he has been giving Mantz the only thing he has—his time—for $1.25 an hour so Mantz can have a big house and everything else he wants. Mantz doesn't argue, and when Henry demands unemployment insurance, Mantz promises he will have it and tells him to get the hell out.