Robert is an ideological villian. That is he is a villian because of what he believes in, not because he's 'evil' or insane or just plain mean. Robert believes in the ability of the Terram to win out over all others and this is what drives him to continuously pursue Kei, even through setbacks and defeats. Robert never gives up and this becomes almost an obssession by the time he meets his end. Ironically, Kei does not kill him. It's a dead center shot from Mome manning one of the Glomar's guns that sends Robert to his fate.