Though Kenneth Branagh is perched at the top of his game — both in directing and acting — 10 years ago he had serious doubts.

The star of such films as “My Week with Marilyn” and “Hamlet,” and the director of movies like “Jack Ryan: Shadow Recruit,” “Cinderella” and “Thor,” Branagh could paper his house with accolades, throw in a knighthood, a theater company and a panoply of memorable performances.

But he says, “I found in my 40s a time when I found acting extremely difficult and very pressurized. And I didn’t want to quit, but I had to get over the hump of it. It began when I was playing in ‘Conspiracy’ for HBO.”

“Conspiracy” was about the meeting of Nazi officials held to determine the “final solution for the Jewish question.” Branagh played SS Gen. Reinhard Heydrich, the leader of the conference.

“It lasted for quite a few years where it was much harder to lose yourself in a character,” he says. “It started there because I didn’t want to be part of that man’s psyche, and it felt like one became rather self-conscious about what one was doing. And really, where I rediscovered joy with acting was when ‘Wallander’ began.”

“Wallander” is the PBS series on “Masterpiece Mystery!” about a melancholic Swedish detective, filled with quiet desperation as he observes the worst among us. The final three episodes begin airing Sunday.

“In a way it was because you stripped artifice away, and you became very comfortable with being uncomfortable,” he says. “You realized that to play something like this it just wouldn’t or couldn’t be easy. Just trying to present the truth under the unflinching gaze of the film camera, you had no choice but to commit. And somehow it put me out of the other side of a period where I’d been just not enjoying it for a long time, still committed to it, but finding it very, very difficult.”

He says he began to ponder the meaning of his work. “Sometimes you have to shake yourself down to understand how a piece of entertainment can be quite meaningful to people, or at the very least, enjoyable and diverting. And this is not a bad thing to be able to do. I think during that time, I lost a little that sense of purpose, in a way that sounds like it’s ego-led about legacy, but it’s more about finding a purpose.”

Branagh was born in Belfast. His mother worked in a tobacco factory, his dad was a plumber and carpenter. “It was a working class district of Belfast,” he says. “We lived in a very small house. We were working class rather than poor. We always had clothes and food. There were tangible moments in my childhood when I knew there wasn’t — that they were having a tough time.”

But Branagh harbored the spark, discovering acting at 16 and studying at the Royal Academy of Dramatic Arts. He was just 28 when he directed his first film, “Henry V,” earning two Oscar nominations.

And it took all those late- night rehearsals, the hours of grimacing for the camera to prepare Branagh for “Wallander.” It’s a quietly subtle performance, much of it a map of human emotion traced across his face. “Sometimes with characters you can be more honest, more direct, more courageous than anything you might be in your own life,” he says.

When he began the second series of “Wallander,” he was preparing to direct “Thor.” Those two projects were immensely different, says Branagh.

“For me it was a tremendous counterpoint to be involved in the internal journey of a character where it’s a solitary occupation but a very engaging one if you’re an actor. Your imagination is very keenly engaged with what the character is going through, in contrast to captaining the great ship of logistics that is a huge movie like ‘Thor.’ So for me the difference in scale, size, intensity and group or solo activity — ‘Wallander’ was always something I ran back to because the requirement of the character seemed simpler.”

When he says “simpler,” he doesn’t mean less complicated. “It’s the idea of the refinement; reducing the sauce in cooking. I believe that simplicity is absolutely the hardest thing to achieve, to take those layers away and try to present something as raw (as the character). As soon as you drive over the bridge from Denmark to Sweden with this particular story — there’s a town full of very happy people in Ystad, they’re not all sad.

“But the combination of these books, that character and going there, by the time you got to the house I used to stay in, I’d go in the door and go in the bathroom and look in the mirror and go, ‘Christ I’ve aged literally coming across the bridge.’ And each time I finished playing Wallander, literally, I would go straight to the makeup caravan and we’d cut everything off, shave the stubble, put every positive unction on your face, I’d go for a swim, just literally wash that man right out of my hair.”