Former Blackguards
Although it is highly unlikely, some blackguards can be redeemed, feeling thoroughly ashamed of what they have done. Such blackguards are in the minority. Those who do repent tend to be ex-paladins or other characters of good alignment. Although an ex-paladin can never regain his status, one who became a blackguard and then abandoned that class often fights evil harder than even the most fervent of true paladins, because they realise what they have lost and are more anxious than any other being alive to atone.
Rarer still are the ex-paladins who became blackguards, had an attack of guilt, gave it up, reformed and regained their good alignment and fervour, began to fight evil with a level of utter loathing and cruelty that meant they stopped being good and backslid into evil, trained as assassins as a means of fighting their former masters, had another attack of conscience as they realised what they became, turned good again... and at this point the writer needs an aspirin. Or a large shot of chlorpromazine. Or, for preference, both.
Evil
Like assassins, all blackguards are evil. They may be of any evil alignment, although they tend to base their preference on their other classes. See the table in page 2 for details.
Lawful Evil
The lawful evil blackguard is meticulous and disciplined. They devote their life to evil, with an emphasis on the tyrannous and the organised side of villainy. They have few vices, form complex plans and stick to them. Lawful evil villains seek to control, forcing others into the same kinds of thought and worship. They are perhaps the least selfish of the blackguards, prepared to lay their own lives on the line in the name of their cause, although they are well aware that the system they follow benefits them. Their values are a corruption of the paladin's ideals – they are just as lawful as their enemies, but they twist interpretations of laws around themselves, and ensure that the common good does not benefit from such work.
Evil Outsiders contacted: The outsiders most commonly contacted by lawful evil prospective blackguards are devils, although supplicants may also contact barghests, efreeti or rakshasas if they prefer unconventional allies.
Neutral Evil
The neutral evil blackguard is the ultimate pragmatist. They look out for number one and are devoted to evil, but have no especial love of law or chaos: whichever method works best to achieve their ends is deemed acceptable. They are treacherous and vindictive, although one cannot expect them to be immediately treacherous, since their plans may already have accounted for expectations of such duplicity. Selfish masters of second-guessing, neutral evil blackguards are perhaps the very worst of their kind.
Evil Outsiders contacted: Night hags possess a great wealth of dark knowledge and are often contacted by blackguards. Nightmares are another good choice of demonic contact.
Chaotic Evil
Chaotic evil blackguards are difficult to predict. If the lawful evil blackguard's ideals are a corruption of the paladin's virtues, then her chaotic evil counterpart's tenets are the diametric opposite. Some routinely indulge any vice conceivable; others are cowards who retreat and expect minions to do all the fighting. They have no regard for any rules or rights, taking their 'might makes right' ethic to the extreme. Often rapacious and sadistic, occasionally insane, the chaotic evil blackguard's deeds are the greatest affront to the paladin and her allies.
Evil Outsiders contacted: The prospective blackguard almost always communes with demons.
Blackguards in popular fiction
I guess at this point I could launch into a lengthy discussion about which characters in the fantasy novels and which aren't… but for some bizarre reason, I don't really feel like it. I'll just fire a few brief shots off, though, just to give you a few reference points and perhaps provide a few atoms of inspiration when designing your own blackguards.
- The Nazgûl from The Lord of the Rings: nine aristocrat/fighters who were corrupted by an outsider (Sauron), got some blackguard levels and then became undead.
- Venger from Dungeons & Dragons: a lot of spellcasting ability, probably a sorcerer; then was corrupted (according to the screenplay for Requiem), becoming a blackguard. Probably corrupted by an outsider of some kind (we see his master in Dungeon at the Heart of Dawn). This had the unfortunate side-effect of making him a transvestite. He wears the same stuff as his sister Karina.
- Mumm-Ra from Thundercats. Mummy cleric/blackguard. He's got a fiendish dog as a servant (Ma-Mutt) and has outsiders as contacts (the Ancient Spirits of Evil).
- Skeletor from Masters of the Universe is yet another example of a blackguard. Starts off as a fighter/wizard. He was pretty corrupt from the start, was trained by an alien called Hordak (close enough to an outsider for our purposes), has a fiendish servant (Panthor)… do you sense a pattern here?
And so the list goes on. I could go on all day, but I'll stop before I annoy you all by proving that Zorak from Space Ghost: Coast to Coast is a blackguard as well.
Conclusion
The blackguard is a tried-and-tested villain – he's always been around in some form or other. In earlier editions it was an anti-paladin. Before then it was just an evil fighter or magic-user. If you get your ideas straight a blackguard makes a great addition to the campaign. Just make sure that when putting them in you make it easier for the players to suspend disbelief. The biggest obstacle, really, is the ex-paladin. We all know that fallen paladins make terrific blackguards, but if you can, resist the temptation to make every blackguard an ex-paladin, since it'd have one Hell of a knock-on effect on your campaign. If in doubt, make him a fighter instead unless you want a major theme for the adventure to be how good creatures have been corrupted or destroyed.
Never underplay the idea of temptation, too; if you have a paladin in your adventuring party, offer him every chance to become a blackguard or at least become corrupted. Test the character at all times; throw temptation in his path. The blackguard should take the time to justify himself, and present the biggest, juiciest piece of bait conceivable – turning evil gets quick results; it's the easy path. If the paladin starts taking ranks in Hide, you'll know you've got him. Of course, if he actually gets round to taking blackguard levels then you'll have to show him the consequences of his choice. His old temple will be out for his blood, and the PCs will be guilty by association.
Of course you could just end up with a load of PCs who decide that it's cool to be evil. Then you're on your own. Sorry, mate. Your campaign's fucked.
On a final note, almost anyone can be a blackguard; even a commoner with 13 Strength, if he picks the right feats and skills, could be one by level 12. Now there's a scary villain idea...