Raziel:
He is the guy you play as, he's the only person you can play as.

He (Like his brothers) is the leader of his own clan of vampires.
< -- Raz has one hell of a Mouth on him!
At a point in the game he discovers that his whole clan has been killed.
< -- This undoubtedly my best pic!
All vampires go through a state of change (Evolution) where they enter a dormant stage (Like Hibernation)
< - - Another "Before" picture.
and emerge with new abilities and/or physical attributes,
< - - Another "After" picture.
explained in the introductory F.M.V/Mini-Movie, he changed before he was supposed to, and for that Kain ordered him to be killed. That's when the Elder god decided to step in.

The Elder god:
He is the guy responsible for resurrecting Raziel, he explains what to do and why he brought Raz back from the dead.
He could look like an octopus since in the very first room if you look around there are octopus tentacles all over the walls.
At verius points in the game he will tell you what to do, where to go and sometimes how to pass complecated looking obsticles.

Ariel:
After you first beat Kain Ariel appears to you and tells you a bit about herself, that she has been haunting the pillars of Nosgoth for a very long time. 
Ariel was the original balance gurdian. There are giuardians apointed for each piller. When a bunch of guardians got killed, including Ariel. At the precise moment of Ariel's death a baby was born who was called Kain, because of that, destiny decreed that Kain would take over from Ariel as the new balance guardian. When Areil's partner, Nupraptor, found her corpse he went insane, sowed up his eyes and mouth in a bid to cut himself off from the world, and went into hiding. (Nupraptor's retreat)
Ariel haunts the pillers because Kain refused to kill himself and purge nosgoth of vampires.

< -- Damn! what the hell ran into her!
Ariel (Like the Elder god) also helps you by telling you what to do and where to go.
< - - Here is an artist's concept, cooll!
She looks like a floating lady with no legs & half of her face looks like it's been ripped off (Like Two-Face from
Batman Forever)

Melciah:
The first boss you got to kill, he (Like all his brothers) communicate by Telepathy.
< -- Melciah shishkabob!
When he does open his mouth it is usually to roar.
< -- A face only a mother could love, or not!

He has the ability to go through gates (Like the T-1000 in Terminator 2). You can't hurt him directly, he just laughs, his death is probably the most gory in the game.

Kain:
His legacy is what this game is based upon

(Duh!, that's why it's part of the title) First explained in Blood omen: Legacy of Kain he was a vampire who could change shape Wolf, Bat, Mist or normal (Vampire).

He looks like he has cracks all over his face. He has an ear-ring and long snow-white hair tied back in a loose ponytail and was the one responsible for turning Raziel and his brothers into vampires, they used to be priests called the Cerefan.

Kain has the ability to teleport and uses his mouth to talk, as aposed to Raziel's brothers who use telepathy.

You have to fight Kain twice!

Zephon:
This "One ugly Motherf(BEEP)r!" looks like a cross between a Spider and the Queen Alien.

If you hit his Abdomen he lays an egg and once killed gives you the ability to climb walls.

Turel / Morlock / Tomb Guardian:
This guy guards the tomb of Serefan. There is some speculation that this guy was left out of the game and is not a boss, I know now that he isn't a boss because Turel's in Defiance. You do inherit an ability by beating him, although not from reaving his soul - rather from an artifact he was guarding.<
The storyline to this game was changed something shocking just before completed production, he at least looks like a Turelheim resurrected (with the blue aura)
He has to be at least a Turelheim because he has Turel's symbol on his back, plus he is the only Turelheim vampire that talks to Raziel, although he might just be a normal resurrected Turelheim.
You get the Projectile after killing him.
Turel, alongside Dumah, was one of Raz's brothers who killed him.

Rahab:
This guy and his clan has, over the centuries, built up in immunity to water (Can swim, (In it his clan & him are invincable))
< -- Don't try mooning Rahab, it won't do a thing!
Rahab is weak against sunlight, has the Projectile ability and after killing him you learn to swim.

At: http://www.demonolatry.com/vault/hierarch.htm
under Misc. Medievil Hierarchies it says Rahab is the prince of the oceans, coincedence?
Or maybe the game designers went a little bit overboard with thier research? You make the call.

Dumah:
Dumah has the ability to constrict. When you approach him for the first time you take out stakes that vampire hunters have put in him, he comes back to life. After killing him you get the constriction ability.
He was the other guy who killed Raziel.
At:     http://www.demonolatry.com/vault/hierarch.htm
under Misc. Medievil Hierarchies it says Dumah is the commander of the demons of Gehenna. Wherever Gehenna is!

Malek (The missing brother):
Nothing is known about this guy, apart from that he wasn't resurrected from his tomb in the tomb of Cerefan. There are speculations that the creators of this game didn't put him in because they simply didn't have the time.
I learned somwhere that Malek was defeated by Vorador twice then his soul bound and rerstricted to a set of armor.

Mobius:
A very mysterious character. Not much is known about him, he is a time streamer (whatever that is!), he has an eaght on his forehead (I think it's supposed to be sideways as a sideways eaght is the symbol for infinity)

You come
across his statue at a point in this game
and see him in the ending

(click here to learn what happens in the ending)

In the end he also narrates a paragraph of writing.

Name meanings:
I got the following from some guy's post at gamefaqs.com
If he/she sees this, please Email me your name (solidbat@yahoo.com.au) so I can give you credit :)

RAHAB:
The so-called Angel of Violence, also called the angel of the sea and an angel who suffered from an unbelievable pride.
According to legends surrounding Rahab, he was around at the very Creation of the world, with powers over the seas.
He is also mention in the Book of Job. He is at times identified with the fallen angels (or devils) Leviathan and Behemoth,
two dreadful beings of the sea. Rahab is also considered responsible for rescuing from the waters the Book of Angel Raziel,
which had been given to Adam by Raziel and then stolen by envious angels who threw it into the ocean to keep Adam from reading its secrets.

RAZIEL:
An angel, called the angel of mysteries, who is the possessor of a staggering amount of information on all matters secret,
arcane, and mysterious;
his knowledge stems from the fact that he traditionally stands at the very curtains separating God from the rest of Creation and hears and notes everything that is said or done around the throne of the Lord. The angel supposedly wrote down much of this incomparably valuable information in the famous tome called the Book of the Angel Raziel.
This grimoire (a type of book said to contain occult and arcane knowledge related to spells and sorcery) was probably written during the middle ages by one of the Jewish scholars-such as Isaac the Blind or Eleazar of Worms-but this did not keep it from becoming surrounded by a host of legends and tales.
The most notable story is the one that has Raziel actually giving the book to Adam.
The Book of the Angel Raziel is reputed to contain the 1,500 keys to the mysteries of the universe.
Unfortunately these are written in a language so arcane and impossible to decipher (without presumably the aid of Raziel) that not even the greatest angels of heaven are able to figure it out.
He is additionally the reputed chief or prince of the order of the erelim, the Hebrew understanding of what was later called the order of thrones.
For his compassion and concern for Adam, Raziel is ranked as the special patron for the first human.

DUMAH:
Also Duma, the angel of Egypt and the angel of silence.
Duma, whose name in Aramaic means "silence," is often cited as the angel recorded in Jewish legend who appeared and terrified the Israelites as they departed Egypt under the leadership of Moses.
As the patron angel of Egypt, Duma made certain that no lasting harm came to the nation under his authority.
As Jewish lore declares that all of the seventy guardian or patron angels of the nations fell-with the obvious exception of Michael, archangel and patron of Israel-it is possible to count Duma among the fallen angels.
In one Jewish tradition (that of Zohar), he is now prince of hell, with command over a host of angels of destruction and a great number of demons and authority over punishment of wicked souls.

MALIK:
In Islamic lore,
a righteous but nevertheles truly frightful angel who has authority over all of the damned souls in hell and who guards and watches over the infernal land suffering (the name means "master" or "king").
Malik and his able companions torment the damned souls and respond to their pleas of mercy by observing.

ZEPHON:
Guardian prince of Paradise.
The sixth sefira, one of the cheribum.
Gabriel sent Zephon along with Ithuriel to find Satan.
The found him in the garden of Eden while he was tempting Eve.

TUREL:
Turel means "the Rock of God", he is the messenger of Sachiel the Angel of justice,
he is also a one of the "observers" group of angels who descended to the Earth to cohabit with the humans to give knowledge them as the metal forge, astronomy, among other abilities.
These observers have a strange dualidad according to certain interpretations, for many, these are Angels Fallen,
that would become of hell after to have left the grace of God when copular with the human women; for others,
these angels are angels that have helped the humans to acquire survival means.