Now, I never said Wario wasn't an asshole. He definitely is one with the way he operates, I just don't think he's a heartless bastard. Being an asshole and heartless aren't synonymous.
Either way, I think we have vastly differing views of Wario in our head. I suppose that's what make Mario...
I think the thing about it is that Wario isn't heartless, he's a greedy jerk, but he has a heart of gold to some extent. If that wasn't the case, I doubt he'd have any love for a pet like his hen to a point he would drop his quest for a moment in WL2 just to make sure she was alright.
Money...
As everyone has said, greed is definitely his most defining thing first and foremost, but Wario being so driven is something that defines him to me. He gets his ass beat in SML2 and decides that if he can't steal a castle... he might as well go on a journey to get rich enough to own one of his...
Honestly a hard choice. I love the ugly ass style of Wario Land 4, and 1-3 have an interesting style themselves. VB is crazy though, they look so high quality. You can really see Wario's muscles in action.
Me and a friend during a VC did discuss the idea of them doing a Odyssey or Bananza style game for Wario, which I hope is a genuine possibility. Anything to get Wario some platforming+fighting action.