Umbra is a devastatingly powerful sword found both in The Elder Scrolls III: Morrowind and The Elder Scrolls IV: Oblivion. The sword has been known to control it's wielder, turning them into a killing machine. It has a Soul Trap enchantment on it.
 In Morrowind
In Morrowind, Umbra can be taken from an Orc (who is also named Umbra). The Orc wields full Orcish armor, so he is not to be trifled with. Defeating him will allow you take both his sword and armor. Umbra is a two handed claymore.
 In Oblivion
In Oblivion, Umbra is in the hands of a female Bosmer (again, named Umbra), who lives in Vindasel. She is perhaps harder than the Orc in Morrowind as she wears full Ebony and remains at a static level of 50. Defeating her will net you her armor and sword. Unlike Morrowind however, in Oblivion Umbra is a one handed longsword. Umbra also has the highest raw damage of any one handed longsword in the game.