GLaDOS may be named for the real life Dr. Gladys J. Loring who was one of the psychiatrists who evaluated Mercury Astronaut candidates at Wright-Patterson. These men were put through extreme tests that pushed the boundaries of ethical testing.
The development team was quite small and because of this the team utilized assets from the Half-Life universe. To avoid confusion the team decided to integrate the story of Portal into the Half-Life story.
Portal was a big influence for The Stanley Parable (2013). It contains the whole first level of the Portal game as one of its possible endings, and even includes Portal's well-known door-glitch in its story line as an Easter Egg.
In the game files there is an unused Red Portal and a texture file for a second Portal Gun but what function these would have had is unknown.
The developers added Hoopy the Hoop to the game in an attempt to create a popular meme. They later admitted that it was a mistake, because they have completely underestimated the potential of the cake, which would become the meme instead.