, pretty much the archetypal "Dark Lord" common to fantasy and an inspiration to countless BBEGs. We love you big S! :D
The Big Bad Evil Guy, typically shortened simply to BBEG, is roleplaying gamer slang for the primary antagonist of an adventure or campaign. He is the one ultimately responsible for whatever shit his associates or minions do, and defeating him usually means the successful conclusion of a campaign (or at least a part of it). To ensure that this is sufficiently dramatic, DMs often make the BBEG a powerful character, making this final encounter something of a boss fight. The BBEGs seem to know this is coming, so they will usually construct a suitably impressive lair for the suitably dramatic confrontation to take place in.
Many of these fantasy villains often like to address themselves as 'The Dark Lord' or add 'Dark Lord' before their name, just in case you goblin-fondling peasants weren't paying attention to who they are.
Hilariously though the sheer incompetence of some of these big bads is at times a beauty to behold, as their over-arrogant natures, the stupidity of their minions, or luck and/or skill on the part of their opposition means their plans fall apart dramatically. For example Harry Potter, despite being a teen and knowing as much magic as a mouse for most of the series, time and time again foiled Voldemort's plans. Despite having control of one of the key factions in 40k, Abaddon has failed to get anything done in 10,000 years. And yet how do they get with so much failure when they would have roasted their henchmen alive if they had done the same? Simple; if you dare to mention it to their face about their joy-to-watch failures, YOU will be roasting on a fire!
In most video games the BBEG is usually the final villain which you and maybe a couple of hanger-ons have to defeat to win the game. Whether it will be a hard fight or not depends how merciless the game designers are feeling.
Paladins are automatically required to attempt to offer the BBEG mercy, even if they had happily slaughtered hundreds of relatively much less evil minions on their way to the BBEG's lair.
 Requirements to become a BBEG
1. Kill a lot of innocents (unimaginative but kind of a must-do on the list, a tradition).
2. Make big grandiose plans that also include big holes in them, just enough for someone to mess up if needs be
3. Surround yourself with minions and right-hand men. Your evil metre goes higher the more bodies you can pile up there
4. Have a characteristic to define you from the masses, like a menacing eye (Sauron), the ability to shot lighting from your hands (Sidious) or an embarrassing track record of failure no-one can mistake (Abaddon).
5. Perfect evil laugh and twisted sense of humour.
6. Have a super bad ass evil lair
7. Don't melt into goodness at the sight of baskets of kittens or puppies.
8. Pretend you don't have any possible mental problems even if they are there
9. Beat up anyone that even looks like competition.
10. Be a dick to everyone even your own side (tough love).
11. IMPORTANT: Do something memorable. It is not enough to just do all of the above, you need to really do something unique to set yourself up from your peers. Sideous masterminded the complete destruction of the Jedi and the rise of the Sith to masters of the Galaxy. Sauron helped fuck up his world and make a lasting legacy of evil by creating so many evil races. Vect established the single most unpleasant city realm in the galaxy and allowed the Dark Eldar to flourish as a people. What will YOU do to get your enemies quaking in jealously and respect?
 The Big Bad Evil Guy Hall of Infamy
An honour bestowed only to the most truly deserving head honchos of villainkind, not just any hireling with ideas above their station can get here!
- Sauron (Lord of the Rings): The dude who originally created the term 'Dark Lord' in modern high fantasy and was willing to get stuck into the action himself too.
- Archaon (Warhammer Fantasy): Elected bro for life of the Chaos Gods and doer of getting shit done, Failaddon lives in constant terror of Archaon getting fed up and coming to kick him out of existence
- Darth Sidious (Star Wars): Creepy old freak who single-mindedly engineered the complete destruction of the Jedi Order and turned the galaxy on its head so he could rule it as a tyrant (and maintain the massive military industrial complex necessary to combat the Yuuzahn Vong upon their inevitable arrival into galaxy... much like another famous Emperor. Unfortunately not everything transpired according to his design). His favourite trick was using his force lightning to make toast (always too overdone).
- Asdrubael Vect (Warhammer 40k): More dangerous then Failabbon could ever be even in his dreams, Vect passes the time causing countless millions to be tortured, just for his bored amusement. Master of dick moves and getting others to get others to do his dirty work.
- The Timeless One (Halo): AKA The Flood and The Gravemind, came from a race of nigh-omniscient Eldritch Abominations that came before the Universe was born. Single-handedly destroyed a Culture-level Civilisation for shits and giggles, and is now coming back in the form of a horrifying fusion of The Thing, Tyranids and X-Parasite; so that he can force every single living thing in the Universe to "join" him in a very fucked up version of Communism, via OM NOM NOMING their bodies and souls in eternal torment and pain.
- Dracula (Castlevania): Was the big bad in the majority of the Castlevania games (Subverted for the two recent games), how bad is he? Well....when even Death considers him as "Boss", then it should tell you the power differences here in pure EVIL.
- Voldemort (Harry Potter): The big bad evil wizard of the HP setting Voldemort spent most of the series as an evil spirit before coming back in a body made from a mixture in a cauldron (as you do). Countless times he failed to kill the boy who lived and twice he failed to take over the wizarding world, making one wonder about his track record.
- Jadis, the White Witch (The chronicles of Narnia): The white bitch likes to freeze everything and turn you to stone at the drop of a hat if you displease her. She froze Narnia to be her perfect place but was kicked out by a gang of motley kids and their pet cat. Since then she has been hiding on Earth under the guise of Sarah Palin (you thought the love of cold weather and evil politics was just coincidence did you??)
- Matt Ward (Games Workshop): Dark Lord of Fluff Rape and Codex destruction, his plan to unleash his hordes of ultramarine servants to take over the galaxy in a wave of blue and to subject the grey knights to eternal ass rape means few, if any are as diabolic as this man!
Antagonists with crazy schemes of megalomaniac conquest and revenge upon the world, their lairs full of traps and minions...Ian Flemming might have been a good DM.
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