Tarchamus the Unyielding was a legendary Netherese arcanist who lived approximately 5,000 years before 1478 DR. Tarchamus was so powerful he was able to directly harness the power of other planes to rain destruction on his enemies.
He didn't particularly care much for his fellow arcanists and frequently argued with them. One feud with the arcanist Arion grew so vicious that Tarchamus created a spell that opened a gate to Phlegethos to create a volcano that destroyed the floating city of Tenish.
After the destruction of Tenish, the most powerful arcanists led by Tarchamus' friend Emrys banded together and found a way to block Tarchamus' access to the Weave. After his magical powers were revoked, Tarchamus built a huge library inside a mountain. Since he was unable to access the Weave, he was unable to achieve lichdom but was somehow able to transform himself into an extremely powerful mummy with the help of his apprentices. He was also able to transfer most of his consciousness into a magical book, the Book of Tarchamus.
Tarchamus physical form was destroyed in 1478 DR when the tiefling Farideh, her master Lorcan and friends found the volcano spell and used it to blow the top off the mountain and destroy the library. Tarchamus' consciousness lives on inside the book, which fell into the possession of Tam Zawad.