Characters - Niwa Daiki
We never really know what Grandpa's name is until, about, WAY later on in the series. Think towards the end of Stage 2. But I digress.
Grandpa is the one responsible for the kaitou education of Niwa Daisuke, his grandson and 'heir' to the glorious (?) job of phantom thief of the decade. >_> Or four decades, in this case, since Grandpa didn't have a son to run around wreaking havoc at night. :3
Grandpa is a funky guy. He seems pretty goofy and lost most of the time he actually *does* appear in the manga, but on the other hand, he shows some pretty cutely sensitive sides as well. ^_^
When Grandpa was Daisuke's age, he turned into Dark as well... but unlike Daisuke, Grandpa performed his kaitou tasks just as one would go about doing household chores. He had no motivation or incentive, save preserving the family tradition, and went about it dutifully until he met a mysterious young girl named Kurashina Menou... and his nightly duties took on a different meaning.
You know, I think it'll be kinda freaky to know that your former alter ego is now your grandson's. o_O Grandpa seems to cope with it well, though. XD