Mr Saito played by Jim.
Mr Saito is a Japanese businessman who has hired the others to implant the idea in Robert Fischer's mind to break up his father's business.
Jim is a rather gung-ho roleplayer, interested in action, cool fight scenes, and lucrative spoils over careful consideration or puzzle solving. He frequently acts before he thinks, which includes fixating on his own strange explanations for setting details that the GM hasn't explained yet.
Dom Cobb played by Ben.
Dom Cobb is an extractor, specialising in getting information out of people by luring them into roleplaying games and then interacting "in-character" within the game.
Ben is a thoughtful roleplayer who tries to think through the best course of action within his character concept and the setting. He enjoys coming up with clever ways to justify the success of his plans within the premises of the setting.
Arthur played by Pete.
Arthur is Dom's assistant, who researches game targets and finds rules loopholes to exploit.
Pete is an old friend of Jim's. Jim invited him along to join in this new game. Pete designed a character to maximise all the skills he thought would come in most useful in a multi-level game regression game, at the cost of being Smug, Annoyingly Well Groomed, and Sneaky About Stealing Kisses.
Eames played by Sally.
Eames is an impersonator who often takes the roles of various different characters within the game settings.
Sally is Ben's younger sister. Ben took her along to the game on the first evening when his parents couldn't get a babysitter for the night. The GM quickly gave her a character to play so she wouldn't get bored. She enjoys the make-believe aspect of the game, but has some trouble separating it from reality.
Ariadne played by Annie.
Ariadne is an architect, who designs the game maps and places traps and monsters for the others to encounter.
Annie is an acquaintance of Ben's, who attends his drama classes. She was interested to come along and see what this "roleplaying games" thing was all about, after Ben described it to her as a sort of improvisational acting thing. She is dedicated to playing her character as a real, complex person with motivations inspired by a well-considered backstory.
Robert Fischer is the heir of Phanastacoria, his father's business empire. His main concern is looking after Phanastacoria, and finding out what was in his father's Lost Will.
Yusuf is the team's chemist. He keeps an eye on the other team members as they roleplay and tries to keep everyone out of trouble, which seems to be a very difficult thing to do with so many NPCs around.
Peter Browning is Fischer's godfather and an executive in Phanastacoria. Fischer trusts him implicitly but Cobb is implanting the idea that Browning is after full control of Phanastacoria. Who is right remains to be seen.
Mal is Dom's dead wife. She has spent decades of time in the game, and uses her great wisdom and popularity to haunt Dom and destroy all his plans. How exactly she gets away with this is a mystery.