Just posting this definition to point out that the expression predates Family Guy by decades, having at least appeared in Paul Schrader's 1971 essay "Notes on Film Noir".
Ralph Meeker, in his best performance, plays Hammer, a midget among dwarfs.
Someone who is addicted to obtaining money and building wealth. A money addict and fanatic. Breadheads often work more than one full-time job, and some even participate in illicit activities to "obtain the bread".