Gary wanted to purpose to his girlfriend Stephanie in a special and unique way. So, he commissioned a Portal 2 map maker to create a series of maps that would take Stephanie through to a wedding proposal grand finale. Gary was even able to get Ellen Mclain, the voice of GLaDOS, to help out and deliver a few custom lines. The proposal isn’t until the very end if you’re the impatient type.
(via Portal 2 Marriage Proposal : Stuff I Stole From the Internet)