Sam Richardson was given the freedom to improvise in 'The Tomorrow War'.

The 'Veep' star plays Charlie in the sci-fi action flick and used his comedic experience to bring some humour to the role.

Sam said: "It was pretty tightly written, but I got to improvise a lot actually. My first scene where I'm meeting Chris (Pratt's) character Dan, that's mostly just an improvised monologue.

"(Director) Chris McKay was very open and excited for me to get to play around whenever I could and inject myself into the script."

Sam believes that he plays a comedic character in the movie who goes against the project's serious tone.

The 37-year-old actor told Variety: "I have starred in comedic roles a lot, but I feel like Charlie in this movie is also a comedic role, juxtaposed against the tone of the movie.

"It was really fun and exciting to get to play in this genre, running from explosions and shooting machine guns and being scared all the time. I love action movies, I love sci-fi movies, so I got to be a fan within it as well as participate in it."

Sam also confessed that it was hard work spending months shooting material for the film.

Asked if there were any elements of filming that were more difficult than he expected, he said: "Running through the streets of Atlanta repeatedly and shooting at nothing for, like, so many takes.

"It's funny because when you watch the movie, there's certainly a lot of running and shooting, but it's a fraction of what we filmed. It feels like you're doing this stuff for like five months, and then you're watching like, it certainly doesn't look like of running up a hill and downstairs and through smoke."