Good suggestions... I'm still writing the plot arch so there is no player or even a game yet. I have not dropped any hints nor is anything written in stone.
I had an idea to implement a BBEG in the campaign: A lich who successfully hides behind the public mask of a cruel but effective elderly Judge. He earned his lifetime position legitimately when he was younger, no one knows he's become a lich and he has sufficient means magic (non-detection) and mundane (disguise) to conceal his undead nature and evil identity. He is, most definitely 'hidden'.
The tip of the iceberg of his evil is that he's condemning criminals to death - supposedly to be cremated in the 'purifying fires' - but instead, uses the criminals to bolster his undead army by having his undead minions turn them into vampire spawn, wights, ghouls and zombies which he's using to harass someone, somewhere. He's also enslaved non-undead and keeps them under his command such as the dragon chained at the bottom of a huge pit called 'the City Dump' and charged with incinerating the kingdoms garbage lest he become buried by it. I do not yet know what other evil he may be up to.
That darkside video also clinched it for me... give exposition to the BBEG in all his evil glory, then have the PC's cross the Judge in his mundane identity and think... "Hey, there's something familiar about that creepy guy... his voice... his demeanor." THEN add the idea about finding an item in the hands of the undead army that was given to the judge by the PC's might expose another crack in his concealed identity.
Right now, he's just a generic two-dimensional bad guy. He (lawful) evil because he enjoys holding authority and the power of life and death over others. He cruel streak is nasty and dark (enjoys watching torture). He nourishes himself with the emotional energy of Fear. Yes, he knows he's evil and he feels no remorse. In his lich identity he's depraved, soul-less, and insane. His angry, bitter 'mortal' identity allows him to reign-in and control his shattered psyche... but when he gets 'hungry', the crazy comes out.
I don't know who my players will be or what kinds of backgrounds they have but I'll need to find a reason to TARGET the PC's... not just rely on their inherent 'goodness' to sniff him out and take him down. In the end, I want the conflict of giving the PC's an evil enemy who is a well known and respected public official. no-one will believe them, it will be entirely up to them to find a way to expose him.
If anyone has any other suggestions, I'm still excited to hear them.
Thanks folks.