Peridan

Dragonslayer, also known as Peridan, is an enchanted long sword +2. This weapon deals 1d8+2 points of slashing damage, which is doubled when fighting dragons. It also gives the wearer immunity from fear and restores 1 hit point per round when wielded. It has a +2 bonus to thaco, a weight of 3 lbs and a speed factor of 3. This item appears in Baldur's Gate II: Shadows of Amn. It can be found in a part of the ruins of Windspear Hills, which are only accessable when accepting the subquest Samia's plan from Samia herself. The Dragon Scale Shield is found at the same place.

In-game description
"Long sword +2: Dragonslayer (Peridan) Few dare to create items such as this, for who does not fear the wrath of dragons, and what action would more tempt their reckoning? Yet, at a time lost in Faerun's past, there was a need, and this sword was forged in answer. Tempered by a wizard's skill, this blade protects the wielder from the fear they should rightly feel while staring down a dragon's maw. It also bolsters with regeneration, dispels the trickery of illusions, and dares to do double damage against the greatest creatures of the Realms."