Greg

Greg is, during the course of the Perpetual Testing Initiative dlc, the assistant of Aperture CEO Cave Johnson.

Originally, he was written to appear during Portal 2's main single player campaign, however he was replaced by Caroline prior to release and was considered to be "cut" from the game before being added back in the May 08, 2012 patch.

Overview
According to the The Final Hours of Portal 2, one of the reasons Greg was cut was to eliminate the cost of hiring a new voice actor that only played a small role, instead reusing Ellen McLain to voice Caroline.

Trivia

 * In a line cut of Portal 2, Cave Johnson reveals that Greg had fought a bear at some time in the past.