Gary Oldman spent 200 hours in the make-up chair for his transformation as Winston Churchill in Joe Wright's Darkest Hour.
The Dark Knight Rises star described the role as "a hard one" while he promoted the upcoming film at CinemaCon, and revealed he "carried around half my body weight" in prosthetics to add bulk to his slight frame.
The film's trailer was reportedly drew "gasps of surprise" from the audience at Oldman's complete metamorphosis as the iconic former Prime Minister, according to Deadline.
It's also claimed that the actor has perfectly captured Churchill's cadence and tone of his voice in the biopic, which follows the first five weeks of his reign as Hitler began his invasion.
"We see how very, very close we came to Nazi tyranny," Oldman revealed at a panel hosted by Focus Features at the annual event.
"Had it not been for Winston, our world might be very different. That, in itself, to come in and play those things is a wonderful gift for an actor."
On the various challenges of his roles throughout his career, spanning nearly two decades, he continued: "They're all challenging in their own way but Winston was kind of a hard one.
"It's a lot to wrap your arms around. Not only the physical, but he is arguably the greatest Brit who ever lived... a kind of iconic figure.
"It was daunting but once I started to find out who the man was, it was... Well, I never enjoyed anything so much in my life.. I couldn't wait to get to work and be him."
The impressive cast also includes Ben Mendelsohn as King George VI, Lily James as Elizabeth Nel, and the late John Hurt as Neville Chamberlain.