On the Daedric Princes.

The Daedric Princes, the fifteen most powerful Daedra in existence. Each rules their own plane of Oblivion, each has their own spheres of power.

As stated in a previous volume (- this is Volume thirteen in my translation -) Daedra are forces of change, and this is why Men especially hate them so, for change is in the passing of time, and in the passing of time comes the end of their lives, lines and legacies.

The worshippers of the Daedric Princes are many and varied. Some worship the Daedra as Men worship Aedra, a prayer now and then and a shrine in their honour. Others though, take their faith far more seriously, involving human sacrifice, fights to the death before their chosen Prince's shrine and more.
To clarify, the word 'Prince' is not used in the sense of the son of a king, for that would make the Daedra male, while they have no gender, and also insinuate the existence of a King, a power ruling over the Daedra. It is used in the sense of the ancient Cyrodiliic word 'Princeps', first, as in, the first amongst Daedra.

The fifteen Daedric Princes are, in no particular order, Molag Bal, Meridia, Mehrunes Dagon, Hermaeus-Mora, Azura, Namira, Boethiah, Mephala, Hircine, Peryite, Clavicus Vile, Nocturnal, Vaermina, Sheogorath and Sanguine.

Molag Bal is the Lord of Domination, the creator of Vampires and the King of Coldharbour. He is also known as the King of Rape, as he was the first to commit the heinous crime, and in doing so created the first Vampire.
He is considered to be extremely evil, and attempted to invade Tamriel in the second era.
His Artifact is the Mace of Molag Bal, also known as the Vampire mace. It seems that its powers change throughout time, sometimes being vampiric in effect, stealing life force, and other times stealing energy.

Meridia is considered to be one of the kinder Princes, bringer of the light of Dawn and strong opposer to all undead. Her Artifact is Dawnbreaker, a blade with the ability to light those it strikes on fire and, in the case of undead, cause them to explode in a fiery ball of flame.
She is close to Azura, the Prince of Dusk and Dawn.

Mehrunes Dagon is another of the Daedric Princes considered evil. He is the Prince of Revolution, and attempted to invade Tamriel at the end of the third era, causing the Oblivion Crisis.
His Artifact is a dagger with a chance of instantly slaying any living creature. This is both the most useful and least useful of Artifacts. It can allow its wielder to slay a giant with one slash, but it may also desert you when you most need it.

Hermaeus Mora is the Daedric Prince of Fate and Forbidden knowledge, who rules the infinite library of Apocrypha. The form he takes most is a fearsome mass of tentacles and eyes, and his Artifacts are books. The Oghma Infinium is the most powerful of them, allowing the reader to become far more skilled in either Magic, Stealth or Fighting. His other Artifacts are Black Books, which, when read, take one to the realm of Apocrypha.
It is a hellish realm, filled with accursed souls in the form of Seekers. Should one succeed in finding the Black Book in Apocrypha (s)he is rewarded with an exceedingly useful skill, depending on which Black Book was read. This ranges from the strengthening of your spells or strikes, to making your strikes and spells harmless to those not seeking to harm you.

Azura, the Prince of Dusk and Dawn, who turned Chimer to Dunmer. She too is one of the more benign of the Princes.
Her Artifact is Azura's Star, a great boon to any enchanter. It is the only soul gem capable of being reused.

Namira is the Prince of the Revolting. Her sphere is anything considered to be repulsing to most, slugs, cannibalism and so on. She is neither particularly malignant nor benign. One could even argue for her kindness in sheltering and caring for those that are repulsing to others, but considering they are cannibals, there may be an argument for them being truly repulsive.
Her Artifact is Namira's Ring, a ring that grants more endurance to its wearer, and should the wearer feast on human flesh, will grant him more vitality and increased healing.

Boethiah, the Devourer of Trinimac and Prince of Plots. She is considered evil for her spheres of power, and her priests and priestesses are amongst the more bloodthirsty. The way to summon her is to bind one who trusts you and slay him or her on you shrine.
Her Artifact is the Ebony Mail, a powerful cuirass that poisons those that stray too close and shrouds the bearer in shadows if (s)he desires it.

Mephala is the Prince of Lies, Deceptions and Whispers. She too, is considered evil, and her dealings with mortals often involve treason and betrayal amongst trusted friends.
Her Artifact is the Ebony Blade, a sword that can leech the life force of an enemy, provided it is charged. It is charged by its wielder slaying one who trusts him or her.

Hircine is the Prince of the Hunt and the Manbeasts, the creator of Werebeasts and their God. He is the leader of the Wild Hunt, and when a Werebeast dies (s)he joins him in it.
His Artifacts are Hircine's ring, which will randomly turn the wearer into a Werewolf should the wearer not be one. If the wearer is one, it grants increased control over the changes.
His other Artifact is the Savior's Hide, a cuirass that grants great resistance against magical forces.

Peryite is the Prince of Pestilance, also known as the Taskmaster. He is considered the weakest of the Princes, though his Artifact is amongst the strongest.
His Artifact is Spellbreaker, a Dwemer shield in appearance that can negate spells and even Dragon's Breath.

Clavicus Vile is the Prince of Pacts and Power. His dealings with Mortals often involve making pacts and deals, and then fulfilling them in a way most detrimental to the Mortal. This involves the killing of those wishing for a cure for disease, or an attempt at killing absolutely every single person in a Province to end a civil war.
He is different from the other Princes in that he has a counterpart, a companion, who attempts to curb his more destructive tendencies.
Barbas is arguably one of the greatest daedra in existence; he tirelessly works to limit Clavicus' urges and warns away those who do not understand what they're getting into.
His most powerful Artifact is the Masque of Clavicus Vile, which makes one more respected and loved.

Nocturnal is the Prince of Shadows and Queen of Murk. She controls the luck of thieves. Her most important followers are the Nightingales, three powerful thieves that protect her temple. Her Artifacts are the Grey Cowl of Nocturnal, which disguises the wearer perfectly, and the Skeleton Key, an unbreakable lockpick, which allows even the most inexperienced of thieves to open any lock, given time.

Vaermina is the Prince of Nightmares. This makes her a rather unpopular Daedroth. It is said that when one has a nightmare, he or she is actually brought to her realm of Oblivion.
Her Artifact is the Skull of Corruption, a staff that can harvest the dreams of sleeping Mortals to become more powerful.

Sheogorath is the Prince of Madness and Delusion. His realm is divided into two parts; Mania and Dementia, representing the two sides of madness. Mania is happy delusions, vivid colours, cheerful inhabitants and more, while Dementia is the darker side, paranoia, strife, rage. "The Mad" are divided into many different groups, named in The Blessings of Sheogorath, being the Madmen, Phobic, Obsessed, Addicts, Murderous, Firelovers, Artists, Musicians, Sleepless, Paranoid, Visionaries and Painlovers. Each of these is in some way 'blessed' by the Madgod.
Sheogorath was not always what he now is, once he was Jyggalag, Prince of Order, most powerful of the Princes. But out of fear, the others cursed him, changing his personality to what it now is. Once an era, during what was known as the Greymarch, Jyggalag would attempt to take over the Shivering Isles (Mania and Dementia). This cycle was ended around the end of the third era by the Hero of K'vatch and Champion of Cyrodiil, who in lifting this curse took it upon himself, becoming the Mad God. This means that the Sheogorath we see today is the youngest of the Princes, being but slightly over two centuries of age. Younger than many Vampires and Elves, might I add. The Madgod's Artifact is the Wabbajack, a staff that is entirely random in effect. An attacking wolf may be turned to a rabbit, a rabbit may be turned to a carriage. There is no method whatsoever to it, and it has been known to drive its wielders insane due to that fact (see the book Wabbajack for an example).

Sanguine is the Daedric Prince of Dark Indulgences, and is therefore rather popular. He is quite benign, and can often be found in taverns challenging people to drinking matches. I was once involved in one of these, and found myself waking up in a ransacked temple, having run all the way across Skyrim, accidentally married a Hagraven and in some way utterly annihilated a coven of Vampires. None of which I could remember, though I'm sure I enjoyed it at the time.
His Artifact is the Sanguine Rose, a powerful staff which allows its wielder to summon a powerful Daedroth to fight for him or her.

And finally, as with the Aedra, he deserves mention here.
Mauloch, Malacath, Prince of the Spurned and Ostracised, not truly a Prince, but not truly a Divine either. His followers are the Orsimer.
While he does not truly have an Artifact, he has strong connections to the Hammer of Might, Volendrung, long ago created by the Dwemer.

In any dealings with Daedra, it is most important to remember how insignificant to them you are. They have been around for millennia longer than you, and have seen thousands just like you. You are, to them, a completely replaceable plaything, and your life means nothing to them.

To successfully deal with Daedra you need to know what motivates them, what drives them. How to appease them and how to impress them. This varies greatly between Princes, but here are some tips that I would have found useful, had they been given to me before I met the Daedroth in question.
Meridia hates the undead greatly, and seeks to have them eradicated entirely. Do not, at any time, reanimate a corpse in her presence or while doing something for her. In any conversation with her it is in your best interest to act subservient.
Nocturnal requires strength of will, so it is not useful to prostrate yourself before her. Throwing yourself on the ground is likely to earn you nothing but disdain.
Boethiah is all about desires, and the will to attain them. If you ever have need of dealing with her, be prepared to kill another human to save yourself.
Malacath demands strength, aggression and honour from his servants. A willingness to fight for what you think is right.
Mephala... In dealings with Mephala you are like to be asked to betray one or more of your allies and friends. Her enjoyment comes from tugging at the ties that bind mortals, love, hate, friendship. She enjoys pulling at these binds and seeing when they break.
Hircine rewards strength and hunting prowess. In dealings with Hircine it is likely that many people compete to be the one to kill a beast, and the killer is then rewarded. There are, of course, no rules against killing your opponents while hunting.
In dealings with Sheogorath, beware the mood swings of the Madgod, and don't become overly panicked at the first mention of ripping out (your) entrails and skipping with them, as he is unlikely to do so if you distract him.
When dealing with Clavicus Vile, the best thing to do is stop. Clavicus Vile is likely to either twist your words to suit him or end the deal at a time most unsuitable to you. There are very, very few people who have made deals with the Prince of Power and come off better for it.
And when dealing with Hermaeus Mora, that applies even more. No matter what you do for him, no matter how long or loyally you serve him, you're a replaceable asset to him, and your free will is nothing but a nuisance. His desire is to have you eternally serve in Apocrypha. There is little more that he wants from you.

- From the Journals of the Dragonborn, Volume eighteen.

It seems odd for the time that the Dragonborn so readily admits to dealings with the Daedra, which, this and other writings clearly state, was taboo at the time. I can only speculate that either the Dragonborn was a special case, or that he never actually planned for these to be read.
Of course, the Dragonborn was to fight Alduin the World Eater. I cannot imagine the people being unwilling to grant the saviour of existence at least some leeway.

Authors Note: I would just like to thank everyone who read this, and especially those who reviewed/favourited/private messaged! Once more, should you have any particular topic idea, I'm open to most things. One thing that i most certainly will not be doing a chapter on will be the Amaranth (the next Godhead, in essence, if you remember Volume 3), since that's a topic that dozens of people have spent over six months studying/debating/arguing, and I would only end up confusing everyone (including myself) more.
Author's Note update: Thank you very much Dragon Kaiju Prince for pointing out the fact that I entirely skipped over Sheogorath. I've added him in now, and thank you for your further suggestions for chapters as well!