 As part of her character arc , the plot moves GLaDOS from her anger with Chell for her actions in Portal , which Wolpaw said " was going to get old pretty quick " , to an internal struggle . The reuse of McLain 's voice led to the creation of a backstory and subplot about GLaDOS 's creation . The writers panicked when they realized that their plans to have Chell and GLaDOS play off each other would only work if both players spoke . To remedy this , they created the Caroline subplot to give GLaDOS an external situation to deal with and to drive the story during the middle act of the game . 
