For the new season of “Fargo,” star Ewan McGregor had his work cut out for him. Not only did he have to learn the notoriously difficult Minnesota accent, but he had to master two slightly different versions of it.

That’s because McGregor is playing two roles — brothers Emmit and Ray Stussy, whose years-long feud over an inherited, valuable postage stamp leads to a murder in this latest “true crime” yarn. As we meet them in the “Fargo” premiere (April 19 at 10 p.m. on FX), older brother Emmit, who claimed the stamp as a child, is a handsome family man enjoying his success as the “Parking Lot King of Minnesota,” while Ray is a pot-bellied, balding parole officer out to get his due now that he’s fallen in love with one of his parolees, the beautiful, bridge-playing Nikki Swango (Mary Elizabeth Winstead).

“It’s a very old fable, two brothers fighting over their birthright,” McGregor said in a conference call with reporters. “This grievance with his brother is the reason [Ray] can’t give [Nikki] what he wants to give her. Although it’s a fight over a stamp, the stakes are high for him.

“He feels like his brother conned him, which is a difficult thing to swallow when your brother goes on to have a successful life and you don’t.”

To pull off the dual casting involved a physical transformation on McGregor’s part. Coming off the “T2 Trainspotting” sequel, during which he became an “obsessive runner,” the 46-year-old Scottish actor says he was in the best shape of his life. So to play the heavier Ray, he was ordered to gain weight.

“I just started eating whatever I wanted, whenever I wanted. I made sure I ate carbs with everything and french fries with everything. I didn’t have any technique besides eating a lot,” McGregor says. The actor didn’t track how much weight he gained, but notes, “I couldn’t get into any of my trousers anymore. I went and bought three pairs of Levis with waistbands three inches larger than I usually wear.”

The process of putting the makeup on buys me the time to stop and come out of one character and go into the other one.

Then, because Emmit is thinner than Ray, he wears a Spanx compression t-shirt in those scenes, which also had the effect of straightening that character’s posture. Ray, on the other hand, wears cowboy boots, which gave him more of a sauntering gait. On set in Calgary, Alberta, McGregor often has to portray both brothers in a single day, which starts with two-and-a half hours in the makeup chair to transform into Ray.

“First, I have my hair wet-shaved and I wear three prosthetic pieces: one on the bridge of my nose to make [it] slightly wider, one on my chin that makes my cleft chin disappear and this heavy piece around my neck. Also the moustache and that funny receding, long-hair wig,” he says. “The process of putting the makeup on buys me the time to stop and come out of one character and go into the other one. It’s been very useful. If it was more quick, it would be very jarring.”

McGregor says both characters — Ray’s “lovable oddball” and Emmit’s “soulless capitalist” — are equally satisfying to portray, and he can’t pick a favorite brother. Others involved with the series, however, have chosen a side.

“The crew prefers Ray for sure,” he says. “You can tell that the crew really like it when Ray’s on set more so than when Emmit is.”

“Fargo” Season premiere 10 p.m. April 19 on FX