Greg

Originally written to appear during Portal 2, Greg was a scientist and a friend to Cave Johnson. Though what role Greg may have played is unclear, he was replaced by Caroline before the release of the game. Therefore, Greg may have been an assistant to Cave.

Overview
Greg may have been cut to eliminate the cost of hiring a new voice actor, instead using Ellen McLain to voice Caroline.

Trivia

 * Mel and Greg are the only characters known to be cut from the 'game.