Confirmed on first-party pages
Aidan Lynch is the protagonist. The PlayStation Blog spells his first name Aidan; the demo subtitles spell it Aiden. This wiki uses Aidan throughout and notes the variance here once.
Sunny is Aidan's girlfriend. She activates the Genesis Configuration at the start of the story, and the Cenobites tear her in half. The story's goal is saving her soul, and the Cenobites turn out to be the means of doing it.
The Hell Priest, better known as Pinhead, is the Cenobite whose bargain Aidan has to survive. The dev diary quotes the original film's description of the Cenobites as "explorers in the further regions of experience", which is the franchise's own framing of the character. More detail on The Hell Priest.
Marlowe leads the Scarlet Church. The dev diary describes him as a charismatic figure whose cult wants to establish contact with the Cenobites and use the Configuration to create a debauched paradise. Demo subtitles spell the name Marlo, with the same pronunciation.
Leviathan is the creator of the Cenobites and the ruler of the Labyrinth. Leviathan is the entity that denies the Unworthy, turning them into what the dev diary calls Hell's rejects.
The two enemy factions
The Cenobites are the otherworldly faction, and the dev diary's own framing is that they are not easily read as morally bad. They pursue sensation, extreme pain or pleasure alike, and in this story they are the route to saving Sunny.
The Scarlet Church is the human faction: real people seeking the same enlightenment, led by Marlowe, who will use the Configuration to build their own paradise.
The Unworthy are neither. They are people who sought greater experiences and were denied by Leviathan, now drawn to the box as a possible path back. All three are covered in gameplay terms on Enemies, the box they are chasing is on Genesis Configuration, and the premise is on Story.
⚠️ Unconfirmed. Names seen only in community playthrough subtitles include Charlotte, a cult member undergoing an ascension ritual, Bruno, a butcher carrying a key card, Brother Abe and a figure called Mr. Magpie. These come from a single playthrough with no official cast list to check against, so their spelling and even their roles may be wrong.
FAQ
Who does the player control?
Aidan Lynch, in first person, throughout the story.
Is Pinhead playable?
No source suggests any playable character other than Aidan.
Is Sunny playable?
Nothing official indicates she is. Her role in the story is the person Aidan is trying to save.
How many characters are there in total?
No first-party cast list has been published. Only the five figures above are named on official pages, plus the two faction names.