(note: possible D3 spoilers ahead)
Aptly named Dr. Malcolm Betruger is the main adversary in Doom 3 and Doom 3: RoE. In some audio log it is stated that he teleported to hell and was somehow changed when he returned. This implies that he made some sort of pact with some demons or was possessed by them. However, I was wondering whether he already planned to do so before entering the portal (maybe even before starting to work at UAC) or if he went into the teleporter for some legit (research?) reason and then was corrupted after reaching hell.