The Malthusians are the main antagonists of hydrophobia. They are a group of terrorists who want to stop the population problem. They are also the people who are responsible for the Queen of the World attack. Kate has to fight a large number of Malthusians throughout hydrophobia, they can be killed in many different ways including burning, drowning, electrocution and, of course shooting them. They can fight competently on both land and sea and use a wide range of weaponry.