Cory is Marvellax's
oldest kid. Marvie's had the biggest influence on him, so even though he can't stand his father, he sticks around him. He's got a bit of temper, but it comes in flashes and he mellows out very fast. That's part of Marvie's psychological and telepathic manipulation of his son. The other kids aren't as easily controlled.
Cory's powers are based around him feeling crushed by his father and wanting to push everything away. It manifests as gravity control and allowing him to manipulate the density of objects. That gives him tons of secondary powers like being able to change the physical state of objects. By screwing with the density of water, he can change it from liquid to ice to gas. Unfortunately, Cory doesn't have a knack for doing this, so things either blow up or implode.
Cory has no real idea of his father's plot. His only concern is keeping his father away from his younger brothers, and that's part of the reason he (thinks he) sticks with his father.
Because Cory's part of the Greek clan of demi-gods, his eyes look like silver when caught in the light.