The missing cullen?

so in twilight, the cullen family has distinct family members.
the perky one, the wise one, the sweet one, the vain one, the solemn one, the joking one, the lonely, brooding gorgeous bronze haired one. if you could MAKE UP YOUR OWN CULLEN, what would they be like? a guy? a girl? how do they look? do they have a mate? what's their background? yay creativity!