The "amazing" display windows at Marshall Field were something that "I grew up taking for granted. ... My mom would tell me how she would go there as a child and she was taken care of and made to feel special," a hallmark of Selfridge's approach, he said.
While the words "Ari" and "shark" seem made for each other, Selfridge is portrayed as compulsively charming.
"I don't think he can help himself. He loved life and he devoured it, and valued people and relationships ... and he treated everyone equally, from the guy that worked in shipping to his right-hand man," Piven said. "Ari was the antithesis, and ruled with an iron fist and was incredibly reactive."
"And, my God, they're both so fun to play. For very different reasons but equally satisfying," said Piven, who won three Emmy Awards for his "Entourage" character said to be inspired by talent agency executive Ari Emanuel, brother of Chicago Mayor Rahm Emanuel.
One of the pleasures of switching from Ari to Harry was leaving modernity behind, Piven said.
"I just came off eight years of playing a character that was continuously distracted by his phone and email and everything else," the actor said. "The great thing of going back in time is that you had none of that to hide behind. You're face to face, and actually speak to people."
He may end up juggling the two different worlds. A film based on the HBO series was green-lighted earlier this year by Warner Bros, while "Mr. Selfridge," based on healthy ratings and good reviews during its just-concluded run on Britain's ITV network, has gotten a second-season order for 2014.
Piven, age 47, is eager to continue his English adventure as the retailing legend, but has a confession to make: He's no shopaholic.
"I personally don't have a great deal of endurance for shopping. I think women have that endurance gene: They can go and go and go," he said. "I love to box and can go 12 rounds with very little time in between. ... I may have 25 minutes in me for shopping before I hit the wall."
Lynn Elber is a national television columnist for The Associated Press. She can be reached at lelber(at)ap.org and on Twitter (at)lynnelber.