I watched Breaking Bad much later after its main telecast on AMC. But while it was fresh on TV, I used to see various posters or scenes being posted on various Internet portals and Social Networking Sites. Many of these posters had Heisenberg being addressed, depicted or denoted as a King.
I used to think that Breaking Bad is some series about guy becoming the mastermind of the drug business or empire. The people who come nearest or actually fit to the title of king are Elliot Schwartz, Gustavo Fring and Don Eladio. These guys have everything under their command in their respective field.
But if Walter is compared to them, he remains just the manufacturer. When he starts his own business after Tuco's death, he fails. He ultimately has to work for Gus. After Gus' death, he stays manufacturer in his own business while Mike runs the business. After Mike, it's Lydia. While in this case, if we compare Gus, he doesn't cook, he doesn't deliver, he doesn't manage payroll, he doesn't kill his enemies (except Victor and Cartel, situation demanded it), he doesn't cook chicken. He just owns them all, looks after them, solves problems, earns profits. It actually fits an image of a King.
Then why was Heisenberg addressed as the King? Just because Walter says that he wants to create an empire doesn't make someone a king. He reaches nowhere near Gus' level throughout the series.