Garrett

Garrett is a character that appears in Doom Resurrection, but is also mentioned in Doom II RPG in one of the emails at the East Coast UAC HQ on Earth.

Background
Dr. Garret, confronts a survivor of Bravo Team in June 2145, and presents him with Sam, a flying droid capable of opening doors and hacking computers, so that he can reach the Space Port and look for a way off the planet.. As the Bravo Marine fights his way through, Garrett speaks through Sam, offering him advice, and filling him in on what he has discovered by hacking the bases computers. Eventually, the marine is forced to leave Dr. Garret behind, and Sam sacrifices itself to support a closing door to the spaceship, leaving only the data implicating UAC behind. The marine successfully boards the ship and leaves Mars with a few other survivors.

Behind the scenes
His last name is actually given in the Doom II RPG as Vanderhat.