In the following pdf you see a photograph of the actual authority within the valve team:

HL2DesignProcess.pdf

I guess there is no boss needed to beat anyone, because they see the strongest arguments whether they did a good or bad work right on the screen.

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt