Nosferatu (t-Veronica Virus)
What was once Alexander, the sixth head of the Ashford family. Alexander mutated into a brutal monster after failing to assimilate the T-Veronica virus administered by his own daughter, Alexia. The virus induced tentacle growth and caused the heart to be exposed through the ribs. Venom is also produced inside the body and reacts with oxygen to produce a toxic fog. Nosferatu's lethal nature resulted in it being confined beneath the Antarctic Base for fifteen years.
Considering how much of the plot revolves around family relations—for example, Alexia using her father as a Guinea pig, Steve being forced to kill his own father, Chris attempting to rescue his sister Claire, and Alfred suffering from a twisted complex about his sister Alexia—"family" could well be considered the sub-theme permeating Code Veronica. Try playing the game once more while keeping this in mind, and you may see some things in a different light.