It's kind of hard to explain just exactly what he is like, so I present the musical itself:
http://www.hulu.com/watch/28343/dr-horribles-sing-along-blog#s-p1-st-i0It is 40 minutes long and incredibly hilarious.
I have, however, included something of a summary of him below (in case you don't have the time to watch it, though even watching a few minutes should give a pretty solid idea), however, and my
character sheet includes a lot of information in the Personality, Character Traits, Contacts/Friends, and Enemies sections.
Billy is your run-of-the-mill shy guy who lives an average life, or so it seems. His "alter ego," Dr. Horrible, seeks to improve society by destroying the "status quo because the status is not... quo." His exploits under the guise of Dr. Horrible have included using a trans-matter ray to steal gold ingots from a bank (which, during the "trans-matter event" were liquified, but he points out in his video blog (obviously would have to change that to fit the technology level somehow) that the point isn't to make money, it is to take money), hijacking a van (wagon?) to steal the Wonderflonium in it for his Freeze Ray (not sure what that would have been in D&D terms since it's a totally made-up element anyway), and attempting to kill Captain Hammer at a dedication ceremony with the Mayor.
The entire musical is a little absurd, so some of the things he does are a little odd: first of all, publicly sharing his video blog (which, he discovers, Captain Hammer [his nemesis] and the police [town guard?] are viewers of and using the information there to know his plans and stop him), also working on his evil laugh with a vocal coach, applying to join an Evil League of Evil, being somewhat inept at creating devices (his freeze ray, which basically puts the target into stasis, for instance, originally took too long to charge, leading to him getting a truck thrown at him by Captain Hammer, and then, in its second incarnation, wears off after a few minutes; his Death Ray also malfunctions after simply being dropped, causing it to explode when fired and accidentally kills the girl of his dreams (Captain Hammer fired it in an attempt to kill Dr. Horrible), and he also refuses to kill innocent bystanders (one reason he cites for not battling Johnny Snow, who is deluded into thinking he is Horrible's nemesis, aside from Captain Hammer being his real nemesis, is that the park Johnny was waiting at had children there). Another example of this "mercy" is his refusal to kill a kid who would grow up to be President (according to "Hourglass") or to smother an old lady (both suggested by his friend, Moist, as ways to get accepted into the League after being informed by Bad Horse's minions that he had to kill someone).
To replicate his weapons (his stun ray (which he later upgrades to a Death Ray), his freeze ray, his trans-matter ray, and his Horrible Remote), I was intending to craft wands of various spells that could replicate the same types of effects and then use wand chambers in crossbows to make it seem more like a gun-type ray (in appearance).
EDIT: I'm still debating Lawful or Neutral for the non-Evil component since he is very structured, but he also wants to destroy and replace the current
societal structure.