http://themacgamer.com/2010/05/01/interview-with-marc-laidlaw-writer-for-valve/
TMG: What were some of the inspirations for characters and episodes within HL2?
Marc: We started with the comic stereotypes of Half-Life, absent-minded professors and the like, who are basically science fiction’s ambassadors in pop culture. As we moved into HL2, we started turning them from types into characters, one at a time: Dr. Kleiner is a good example of a character who started as a caricature and eventually became an individual in our game.