Sparda was orginally a baddy working for the evil overlord of the underworld, mundus, until Mundus started to invade the human world. Thus, Sparda took pity on the human for thier breif transeint lives, and so rebelled against Mundus.
Big surprise, he won. Yet he disappeared from earth, but not before leaving his son (Dante) upon the earth to help save it every 2,000 years when Mundus would rise again.
Also the name of an amaaaaazing sword that Mr dumbass Dante left in the underworld for no good reason, yet Trish still gets at the end of the game. (Trish = Dante's mum, or so it would seem. I can't be bothered to get into the long storyline bit here).
1) Hey, I just made Sparda from toilet paper rolls and PVA glue
'goes under as Spardacos, and Lord Sparda also.
"When Sparda joins one side of the War, less you have a death wish you will join as well."