Doomslayer

58 Imperial soveriegns in length from pommel to point. 2 stones and 3 in weight and of exceptional balance and quality. The weapon has no recognizeable gyphs or runes on its angular surface, but it is clear the weapon is above extra-ordinary. As common swords are to coal or ore, an officers blade to polished coral or malachite, a kings blade as to agate or amethyst, the DoomSlayer is to a flawless Diamond or Sapphire. The sword displays no outward sign of imperfection, it is perfect, there are no seams and the blade, guard, grip and pommel appear to be made of a solid and uninterupted material. The blade shows no hint or sign of wear, and draws blood without drawing across the edge. it is crafted of a dark iron like ore, with an almost woodlike grain. The blade is warm to the touch and seems to pulse with a deep and distant feeling throb or ebb of some great force. Those who grasp the blade will immediately be overcome by a gravity that is much greater than their own, and the weapon will seem unnaturally heavy as if they are burdened with a monumental responsibilty.

Doomslayer is surrounded by myth and legend, as it was made in a time now lost. The popular legends has it as a creation at the end of the last era in order to rid the land of the gods that had challenged the age of man; however, it is more likely it was forged in an even earlier era by the very gods themselves. For the gods were greedy by nature and were unwilling to share the world with man. The Doomslayer was forged from the very vein in the world from which man sprouted from, so that man had no power over it. The ancient text purport that men found out of the gods plotting during its creation. Amongst the men a hero came to the inferno and snatched it while the blade still was raw and molten, somehow surviving the holocaust surrounding the blade, and before the gods could react to the would be theft, the hero quenched the glowing blade in the hearts of the dieties. The age came to an end, and so began the era of man.

Currently possessed by the Kathne clan of Elurens. it has been in their blood uninterupted for 500 years, and is passed from warrior king to son. The kathne aren't aware of its origin, but are aware of its dangers, over the years they have formed a bond with a benign local Sun God who guides them into its proper care. The acolytes and priests watch over the blade while it is in the temple, and they accompany the lord when he needs to make of its use.

Addendum
As an amendment to the sword, it does not kill with the touch, but merely gives the ability to kill, what would otherwise be unkillable. it does inflict damage above that of a normal blade (prolly by about 2x). In my system, that is almost grossly powerful in its own right, but In a DnD type system I would probably treat it as a +5 type sword of sharpness, with the added bonus of the dead can't return. (not that anyone has EVER been ressurected outside of necromancy in my campaign) Unbreakable swords can be broken, armor can be pierced (note I say these things 'can' not that they will). And a thrust thru the heart or a lop of the head will end most creatures permanently. (hydras may need more than one head lopping)
When used against creatures like gods or dragons, I'd say the attack is still utter suicide unless you somehow convince the god to let you swing at his unprotected neck, or manage to sneak upon them. (Dragons in my world are MANY fold more powerful than in DnD, Palladium etc)
In my campaign I introduced the item specifically in a quest where there was an unstoppable construct, that was in effect impervious to all mortal attacks (my world is very low magic). In the ensueng battle half of the PCs died, as did many people, and tar-Kathne. The resultant was that on a natural 20 called strike to the heart the Doomslayer pierced the heart of the creature, slaying it. The Doomslayer itself was broken in two (I never said it was indestructable ) The fragment of the Doomslayer was returned to Kathne, where a new generation of Kathne's protected it. The Fore-blade remained embedded in the unbreakable skin of the Construction, possibly for all eternity???

notes
A 'stone' in my system is appx 2 lbs, or 1 Kg, and a Imperial Coin is near an inch in diameter.

Magical Properties:

The blade so far has proven indestructable, as it has shown no wear or corrosion. The edge requires no sharpening and will scratch the hardest materials, even diamonds. It emits a slight whistle when swung through the air.
The true power of the doomslayer is that of its ability to 'unmake' things.
So far no magic, diety, dragon, devil, or godling has shown any ability to resist the edge of the Doomslayer. Simply put it can kill the unkillable, slay the unslayable, and unweave the strands of even the most powerful dweomers.
if the wielder has the will to match, no barricade, no armor, and no blade will provide proof againt injury and the loss of life attributed to the Doomslayer is final and irreversable as the very soul of the slain is itself unmade.

The curse of the blade is such that its power is raw, complete and unchecked, and corrupting. The blade was meant to slay men, and bring civilization to ruination. Only thru the great sacrifice of the hero was the intent of the blade changed and corrupted. And the blade became ceased to be the maker of Doom, but it's slayer and avenger. However, the blade lusts for blood, and to get vengeance on mankind as its intent has gone unfulfilled. With prolonged contact, only the goodliest and strongest willed can resist the urge to begin the slaughter. Even then it takes constanct focus, dedication, and perserverance to overcome the urge.
In addition, all beings of power are immediately attracted to the sword sensing its power. Some will freeze in awe and others will plot to strike the wielder so that they may possess its fury.
In my campaign, one of the PCs, a warrior of strong mind and will, grasped the sword and was completely overwhelmed by the gravity of the sword, and was unable to move, act or think for some period of time. He came to his senses in just the perfect time to prevent his own mortal death. The sword never made to be wielded by inferior beings such as mere mortals.
The blade is also afflicted with a curse non-magical in nature, for the tale of the Doomslayer is well known, and its corrupting ability is absolute. Likewise its good is well known. Any person who attempts to wield the Doomslayer for any but the most righteous cause will be seen by his fellow man as a potential Anethma, a scron on man, and a future ox upon man. The doomslayer is a potential pandora's box in the minds of most. for if surely the wrath is not visited by the blade itself, the anger of the gods it will surely incite.
Forces bent on the destruction of man, or other would be kings and warlords will quest for the blade to accomplist thier malfeance. The blade has remained safe in the mountain monastary of kathne for hundreds of years, hopefully there it will remain.