A couple of weeks ago, Squall posted a very interesting article on zelda-sanctuary.net, where she brings up some examples of how the two demon kings, Demise and Malladus, could be connected. Among the things is that Malladus possibly could be a reincarnation of Demise. Pretty interesting, right? I think the article is very good and that most of her claims are likely to be true. To read the article, click here.

I personally don't think they're connected. Malladus was sealed away in a distant land in ancient times, *long* before Link and Tetra arrived. If Demise's hatred is following them, why would it have appeared somewhere they weren't, much less in a different time period. There's also no way Malladus wasn't sealed before Ganondorf was killed in WW, since there's only 100 years in-between WW/PH and ST. The evidence just doesn't seem to be in favor of Malladus being connected to Demise to me. It's too contradictory.
Malladus probably just replaced Demise or something and instead of going after Hyrule he went for the Spirits of Light
Something about having just re-read the entirety of Homestuck makes the idea of connecting Malladus to Demise very easy to accept as plausible. *lol time shenanigans*
but Ganondorf it he re-incarnated Demise. Watch the ending of Skyward Sword again. >.>
If Demise was a demon king, couldn’t there be a royal family? Maybe Malladus was a relative of his.