Cave Johnson

Cave Johnson is the founder of Aperture Science, which evolved from its precursor, Aperture Fixtures and later Aperture Science Innovators. 

Cave Johnson was not able to oversee all tests going on in the facility, as well as various areas of the facility. So to make up for this, he would communicate through a variety of automated audio recordings from the late 1940s to as late as sometime in the 1980s. 

He has only one line in the whole video. He just tells Doug and Henry to go back to work (though not by name). All this role requires is to pull off a convincing or close enough J.K Simmons impression. Here is a link to his performance as Cave Johnson. https://youtu.be/QLmiknX8bFI