Portal is a puzzle game series released by Valve comprised of 2 games: Portal, released 10th October 2007 and Portal 2, released 18th April 2011. Players must use a device called the portal gun to shoot portals onto walls, so that they can pass through them to complete puzzles. Both games also follow a central storyline around the science facility 'Aperture Science'.

Chell

Chell is the player character of both portal games. She is a silent protagonist and a test subject for Aperture Science, made to complete tests for the sentient AI GLaDOS. She is theorised to be either the daughter of the founder of Aperture Science or a previous employee and her background is not revealed in the games.

GLaDOS

GLaDOS (Genetic Lifeform and Disk Operating System) is the sentient AI running Aperture Science. She has full control over the facility and was created by the employees.

The story of the first portal game is relatively limited. Chell wakes up from a sleep pod to GLaDOS thanking her for being a test subject for aperture science. From there, the player controls Chell through 19 test chambers and cake is a promised reward for completing them all. However, Chell finds something in chamber 16; a den made behind the walls of the test chamber. "The cake is a lie" is written on the walls of the den. In chamber 17 Chell finds another den with similiar writing on the wall.
When Chell finishes chamber 19 she is put on a moving platform slowly moving into a pit of fire which she escapes using the portal gun. From here, she travels through the edges of Aperture science including the old offices of the employees. It is revealed that GLaDOS killed all of these employees by gaining access to a large supply of neurotoxin and flooding the facility with it. Eventually Chell reaches GlaDOS's chamber and has to destroy 4 "personality cores", machines which were invented to suppress GLaDOS's violent tendencies while the scientists of Aperture were still alive, which are attached to GLaDOS as she floods the facility with neurotoxin. Destroying each of these slowly breaks GLaDOS and once they are all destroyed the facility is destroyed (authors note: Wow, I'm sorry I used the word 'destroyed' so much in this sentence lmao) alongside GLaDOS. Chell slowly passes out on the pavement of the parking lot of Aperture while she is dragged back inside of the facility by robot arms.