Unknown (presumed dead)
R. Kasal was a scientist assigned to Mars City.
When the player meets R. Kasal in Doom 3, he can be found working on a console just outside the Infirmary near Marine Command. At the same time, the player witnesses a crazed patient being sedated in the Infirmary. Kasal, however, pays no attention to this incident, and if the player tries to talk to him, he will (like many characters) say he's too busy and doesn't want to be disturbed.
His fate is unknown, though he was most likely killed or turned into a zombie during the demon invasion.