Connection: Edmund (from Shakespeare's King Lear) and Voldemort

Voldemort is the ultimate villain throughout the Harry Potter series. His brutal quest to ultimate power was not meant to be stopped. He connived and killed his way to the title of the "Dark Lord" and didn't stop at that. He wanted to become the most powerful, feared, and unstoppable wizard. His quest would end with him obtaining the Elder wand. 

Like Voldemort, Edmund is on a quest for power. He wants to inherit/ take control of his father's land even though he is a bastard and his younger (legitimate) brother is in line to inherit. He gets rid of his brother Edmund by framing him in plotting his father Gloucester's death. He even betrays his father by telling Cornwall that Gloucester was on his way to help Lear against Cornwall's wishes. This gets Gloucester the punishment of being blinded by Cornwall. 

Voldemort also had family problems when he was younger. he was conceived under a love potion, his dad left before his birth, and his mom died soon after. After growing up in an orphanage and later going to Hogwarts, he later goes on to murdering his father and grandparents for never wanting to care for him. 

This connection between Edmund and Voldemort being ruthless (even to family) in their climb for ultimate power shows how issues with family at a young age can lead to serious problems growing up. Edmund and Voldemort were never loved by their family. Edmund was cast off as the bastard and had to watch Edgar get most of the attention and chance for inheritance, while Voldemort was tortured by the knowledge that his family abandoned him. The power they both search for could be to fill the void left by the lack of love from their parents.