Daisuke Niwa. If you shorten it, it becomes DNA, which is a pun on the Niwa males becoming Dark.

He ends up with Riku because Risa never loved Niwa kun

Die (as in dead) - sue - ke (softly pronouncing kay with not uch emphasis on the Y) then nee - WA

nobody knows, apparently. never seen any pictures myself. or heard of him at any cons either...

Well, the most well known character is Dark Mousy. He lives within the body of Daisuke Niwa, who is probably the second most famous of the series.