I have been thinking about motivation. It would seem that most think Voldemort has some rational motivation for all of his actions. While this seems reasonable in the context of the story I have been thinking, what if his motivations are more personal and emotional than rational.

Imagine you are Tom Riddle^V1 . You spend your life doing increasingly risky things trying to achieve immortality and to stamp out the perceived existential threat that muggles pose to wizards. You stay scared, literal mortal dread at all times even after you develop your Improved horcrux ritual. Finally after long years of heroing and villianing you are killed in an accident but your ritual works, but not quite as intended. You survive the death of your body but getting back into a body is tricky and takes a long time, you are alone with your thoughts for nearly ten years. Now things have changed, you no longer fear death because you have beaten it, what you fear now is something you can do little about because of your previous experience, boredom.

Your desire to stamp out the Xthreat is still there because living alone on a dead world forever would be really fucking boring. You plan complicated games with the only person you thing could ever kill you because your life is dull. You duel wits with mad geniuses while tying your hands artificially with rules like "no legilamancy" because you are bored (this one he mentions specifically after the azakaban breakout). You raise your enemies most powerful and useful companion from the dead and make her all but invincible because he will be less likely to end the universe with her and more likely to make a good opponent for the future.

tl:dr Tom is bored.