It is revealed she was created from the personality of Caroline, a woman close to Aperture Science's CEO, Cave Johnson, who took over the facility after his death.
glados was made by apature science but the conciousness of the character caroline was put into glados.
As all the other people said, GLaDOS was created from the personality of a woman called Caroline who was close to the Aperture Science CEO.
Unrealted to the question, GLaDOS voice was made by a woman called Ellen McLain. This is her portrait picture: