Cave Johnson is a character introduced posthumously in Portal 2 via a series of recorded messages included in the second half of the game. He began making shower curtains and after making his fortune on them moved on to physics research by way of Aperture Science. The Aperture Science Enrichment Center was constructed in an abandon salt mine using a series of geodesic domes. The Cave Johnson era Aperture Science conducted a very eclectic range of research. Genetic testing that led to mantis men, time travel, and of course the portal gun. This was combined with an intense focus on human testing in the form of obstacle courses with the experimental technologies to create a very unsafe working environment. While we really never get enough info to fully understand how Aperture Science operated Cave at one point describes the process as "Throwing science at the wall and seeing what sticks." This science as understood by hyper competitive, technically illiterate, CEO billionaire was pretty effective in the fifties and sixties but ran afoul of Congress after a spat of Astronauts involved in testing went missing. Around the seventies things at Aperture took a turn for the worse and they began recruiting from the homeless population for their tests. Around this same time Cave purchased seventy million dollars in moon rocks to use in the development of portal technology and subsequently discovered major health problems associated with handling them. Cave would spend the last years of his life fruitlessly developing the technology to digitize his mind and while it would come too late to save him that research led directly to the creation of GLaDOS.
Cave Johnson has some of the better quotes from gaming. He's sort of a mash up of the best and worst elements of Howard Hughs, Donald Trump, and Elon Musk being at the center of amazing scientific discoveries with very little grasp of them. He not only bought moon rocks but handled them enough to be badly poisoned by the contact. His company, and by extension he, is responsible for some unknown number of deaths in the pursuit of tests that don't appear to actually serve any purpose. He's also voiced by J.K. Simmons whose voice work is top notch as always. I'll leave you with some of his final words to the player:
"You know, I've been thinking. When Life gives you lemons, don't make lemonade. Make Life take the lemons back! Get mad! I don't want your damn lemons, what the hell am I supposed to do with these!? Demand to see Life's manager. Make Life rue the day it thought it could give Cave Johnson lemons. Do you know who I am? I'm the guy who's gonna burn your house down. With the lemons. I'm gonna get my engineers to invent a combustible lemon that burns your house down!"
IRON NODER XIV: THE RETURN OF THE IRON NODER