David Strathairn likes to portray heroes.

In 2005’s “Good Night and Good Luck,” the Oscar-nominated actor played journalist Edward R. Murrow, who stood up to McCarthyism. In 2012’s “Lincoln,” he played Secretary of State William Seward, who helped the 16th president preserve the union.

Now, in the searing new film “Remember This” — which will make its world premiere this month in the San Francisco Jewish Film Festival — he plays Jan Karski, a Polish diplomat who early on bore witness to the Holocaust and tried to warn the world.

The real-life Karski was by any measure remarkably brave. However, he repeatedly asserted he was no hero.

“Karski considered himself a failure,” Strathairn told J. recently, and he is one to know, having originated the Karski role in a one-man play about him. “He considered himself an insignificant little man. Even in later years, when asked about his heroism, he insisted he was just a messenger, a tape recorder, a witness.”

Strathairn, 73, is slated to be on hand for an on-stage conversation following the film’s lone showing in the festival, at 2:50 p.m. July 24 at the Castro Theatre.

Karski led anything but an insignificant life. Born in Lodz in 1914, he joined his country’s diplomatic corps mere months before the 1939 Nazi invasion of Poland. He served in the army, and later aided the Polish government by slipping into the Warsaw Ghetto as well as a concentration camp, where he witnessed Nazi atrocities firsthand.

He also made secret trips to European capitals, was arrested and tortured by the Gestapo, made a daring escape by jumping off a moving train, met with President Franklin Delano Roosevelt in 1943 and wrote the first report detailing atrocities against Jews. It was ignored. He ended up in the United States, becoming a professor of European history at Georgetown University.

J. The Jewish News of Northern California is a media sponsor of the San Francisco Jewish Film Festival. Check out our full coverage here.

For years he kept a low profile —  until an interview with filmmaker Claude Lanzmann for the 1985 documentary “Shoah,” when he broke his silence and became more widely known. Karski was named by Yad Vashem one of the Righteous Among the Nations, and was posthumously awarded the Presidential Medal of Freedom by President Barack Obama. He died in 2000 at the age of 86.

All of this and more figures into the narrative of “Remember This,” an austere black-and-white re-creation of the stage play. In it, Strathairn deftly plays Karski and many other roles, twisting and turning across the stage in a display of theatrical acrobatics remarkable for someone his age.

“It was invigorating and exhausting,” he said. “What the film does that the play cannot is get in closer and bring the audience right into the performance. Hopefully the film captures the same intensity of the stage piece.”

Playwright Derek Goldman, who co-directed the film with Jeff Hutchens, had worked with Strathairn years before. When the opportunity arose to create a play about Karski on the occasion of the 100-year anniversary of Karski’s birth, the actor jumped at the chance.

“I had seen Karski in ‘Shoah,’” Strathairn said, “and his bearing witness to his experience was indelible, and remained with me. He stuck out. What he said in his testimony was tattooed into my brain.”

After its 2014 debut run at Georgetown University, Strathairn took the play around the world, including a show in Krakow, Poland. And every performance included a follow-up conversation with the audience.

“What’s been most rewarding, moving and illuminating is when there’s someone [in the audience] who experienced the Holocaust firsthand or had a family member or knew someone who survived or didn’t,” he said. “At every performance, there was someone in the audience who could speak to this, and that was a gift to me because it informs the emotional landscape of the piece. It makes it very real.”

Eventually, the creative team behind “Remember This” set their sights on a filmed version, helped by funding from the S.F.-based Jewish Film Institute (which runs the S.F. Jewish Film Festival among other projects).

The story hammers home the futility Karski faced when raising the alarms about the slaughter of the Jews. One prominent Polish Jewish leader in exile disbelieved him, and FDR ignored his warnings in 1943. The late response to the genocide tormented Karski all his life, but in the film, it serves to play up his belief in the unity of humankind.

“He was a humanist,” Strathairn said. “His deep Catholic faith was the purest form of Christianity.”

Though the film offers a raw, searing account of what Karski witnessed, Strathairn believes it’s important that audiences, and society in general, not flinch or look away.

“Revisiting these moments of history, we can give ourselves a leg up, a portal through which to witness our present time,” he said. “It’s a difficult history. People don’t want to revisit these horrors and I can understand why. It takes a toll psychologically and emotionally to reckon, to go back and acknowledge.”

Strathairn, who is of Scottish, Portuguese and native Hawaiian descent, said he is excited to return to his home turf for the premiere. Born in San Francisco in 1949, he went on to attend Redwood High School in Larkspur. His film credits include “Nomadland,” “The River Wild,” and two of the “Bourne” action films. On television, he has had roles in “The Days and Nights of Molly Dodd,” “Alphas,” “The Blacklist” and other shows. On stage he has starred in productions at ACT in San Francisco and off-Broadway.

His performance in “Remember This” enthralled SFJFF organizers. “It’s a tour de force performance on his part,” said Lexi Leban, executive director JFI. “It’s a really beautifully made film. The cinematography is gorgeous. We’re really, really proud of this film. And so I think [the world premiere] is going to be a once-in-a-lifetime event.”

Strathairn said he’s glad to return to his birthplace to launch the new film. He remains a champion of all performing arts, especially in today’s politically and culturally fraught times.

“We need to share [artistic] experiences,” he said. “The arts can be a mediator between divergent thoughts and beliefs.”

“Remember This” (95 minutes) screens at 2:50 p.m. Sunday, July 24 at Castro Theatre, 429 Castro St., S.F.