Playing with fire

BO's Chernobyl is a five-episode miniseries written by Craig Mazin and directed by Johan Renck detailing the Chernobyl nuclear disaster of April 1986 and the cleanup efforts that ensued in Ukraine and neighboring countries.

But as much as the show acts as a historical retelling of the incident, Chernobyl goes a step further than just recounting the swirling emotions and global fallout.
Renck actually transforms the story from a historical drama into a straight-up horror movie to ensure the impact of the catastrophe hits home in ways news reports could never translate for the public.

A Giant Beast

Who
In the film language, the who question is typically answered with the close-up (CU). The primary point of focus in any close-up is the subject's face. This framing typically mimics the experience of what you would see in real life if you were conversing with a person. A close-up is an intimate portrait of someone, more intimate than you would ever get with a stranger. This is part of why fans inherently feel as though they "know" famous actors. (Though the feeling is certainly not mutual!)

Who Are They?: A Close-up gives insight into who a character is.
These shots leave little doubt that one is a no-nonsense sourpuss and the other is a idealistic dreamer.

Close-ups can vary widely based on camera position, lens choice, and other production considerations, but ultimately you can count on such a shot to answer this fundamental question.

If you were to go too long without providing close-ups your audience will lose track of whose story they're following and they will very likely lose interest. This is especially common in complex action scenes where there is so much what and how to convey to move the story forward that it's easy to forget to keep the who present in the viewer's mind. But do so at your own peril. Even the most spectacular battle scene can fall flat if the audience loses track of who it is that's engaged in the fight.