Sean Penn premiered "Superpower", his admiring portrait of Ukrainian President Volodymyr Zelenskyy at war, telling the Berlin film festival Saturday the movie was also a wake-up call about Americans' own fragile democracy.
The two-time Oscar winner was in Kyiv making a movie about Zelenskyy's rise from comedian to national leader when Russia invaded nearly one year ago.
In interviews on that first terrifying night and during the initial months of the onslaught, Penn and Zelenskyy built up what they both call a close friendship.
"It was a very moving way to start to get to know somebody," Penn told reporters.
"Aside from meeting my children at their birth, the highlight of (my life was) meeting and sensing a great human heart of courage that day with that man."
Penn travelled to Kyiv again this week to show the documentary to Zelenskyy and his team. The president's chief of staff, Andriy Yermak, tweeted his thanks: "great film".
Zelenskyy joined Penn by video link at the festival's opening ceremony Thursday to ask for the entertainment industry's sustained help in keeping Western countries united behind Ukraine.
"Cinema cannot change the world," said Zelenskyy. "But it can influence and inspire people who can change the world."
The trained actor stresses in the film that the more quickly the war is ended, the less likely "Americans will have to fight" one day in a Russian war against NATO.
Penn, who appears in almost every scene, said he was okay with being called a "propagandist".
"We made a very unapologetically biased film because that was the true story we found," he said.
The actor admits he was a naive "Pollyanna" before the war, never believing that Russia's Vladimir Putin, whom he called a "creepy little bully", would go through with a full-scale invasion.
Amid gruelling scenes of civilian deaths, the film has lighter moments.
As he heads to the front line in the Donbas region, he jokes when he is handed a knife that the Ukrainian people can now rest easy because "Sean Penn is armed", before brandishing two clenched fists at the camera.
And after months of war, Penn treats Ukrainian air force pilots to a screening of "Top Gun: Maverick" and sets up a video call with one of its stars.
Beyond Zelenskyy, Penn speaks with diplomats, reporters and analysts as well as Ukrainian soldiers and pro-democracy activists to offer an "idiot's guide" to the last decade of Ukrainian history.
The film's title comes from a scene in Zelenskyy's hit comedy show "Servant of the People" in which he tells his young son that he will protect him from "bad guys" using his "superpower" -- his love for his family.
But it is also an ironic reference to the United States and Russia. Penn argues that Ukraine could be now seen as "the better us" -- a new global beacon for freedom and democracy.
"Growing up in the United States -- this won't be news to you -- we are born with a misguided sense of exceptionalism," Penn told reporters.
While America is now riven with political and cultural strife, he found in Ukraine "absolute unity".
"These people are doing what they have to do simply because they love their country and they love each other," he said.
"So the lesson is simple and we should all honour them by doing our best to follow it."
The West, he said, now had an obligation to step up its military support.
"The most significant humanitarian response that can happen right now is the delivery and supply of long-range precision missiles," Penn said.
Initial reviews were mixed, with The Hollywood Reporter calling the project "both vital and vain".
"It would be easy to write the whole thing off as one big and slightly dangerous vanity project, but let's be honest: This war concerns all of us, and the actor is doing all he can to help the good guys."
"Superpower" is running out of competition at the Berlin film festival, which is spotlighting Ukraine with a series of new documentaries and feature films.