The blade's original master, Arva, was killed by Kialandí while defending Ilirea from Galbatorix and the Forsworn. He gave his sword to his sister, Naudra, to defend herself. She escaped to Ellesméra along with another dragon and Rider, both of whom later died. It resided in Ellesméra in the care of Lord Fiolr, Naudra's mate. It is a treasure of the house of Valtharos.
When Eragon sought out a new Dragon Rider's sword, he asked for permission to use Támerlein. However, when he tried out the sword, he rejected it on the grounds that it did not fit his hand and was made for someone with a slashing and hacking fighting style. He also disliked that Fiolr would not allow him to keep it indefinitely. Fiolr was pleased that he did not have to relinquish his hold on the sword. After Fírnen hatched for Arya, Rhunön reworked this sword to better suit Arya's grip. It is unknown how Fiolr reacted to Arya's possession of the sword, however, it can be assumed that he was more willing to give his sword to both a fellow elf and his queen.
The sword was green, the same hue as Fírnen's scales with an emerald set into its pommel. A column of glyphs adorning the cross-guard spelled "I am Támerlein, bringer of the final sleep". It was originally wider than Zar'roc and clearly made for someone with a different fighting style than Eragon, a style more heavily reliant on cutting and slashing. The end was blunt and rounded and the handle was large and used for one evidently reliant on fighting with two hands.
The name "Támerlein" bears a similarity to one of the names borne by Timur the founder of Timurid Empire. The Emperor Timur ruled from 1370-1405 A.D., he was called Timur the Lame or Tamerlane. It also bears similarity to the name of a poem by Edgar Allan Poe.
Tamerlane was the name of a horse in Frederick Forsyth's "Dogs of War".
The name Tamerlein is also the name of a fictional character in the pen and paper rpg "The Dark Eye". Article in the RPG-wiki (german)