The Original Merlin

The original Merlin was a wizard and founder of the White Council.

Proven Guilty
During the time of King Arthur he was custodian of the sword Amoracchius, becoming the first wizard of the White Council to have the honor and only the second in history.

Turn Coat
He is believed to have created the White Council of Wizards out of the chaos of the fall of the Roman Empire, though the White Council has existed in some form since pre-Roman Times.

Changes

 * He wrote the Laws of Magic.


 * According to rumor, he won the Hidden Halls of Edinburgh (the White Council's main headquarters) from the lord of the Daoine Sidhe in a bet.


 * No one is sure how Merlin made out [in the end], but from his journals, he wasn't the kind to go in his sleep.

Cold Days

 * He is also said to have saved most of the critical texts from the Library of Alexandria even as it burnt down, and helped to create the Catholic Church to further preserve knowledge during the European Dark Age.
 * Many stories are told about the original Merlin but many are believed to be apocryphal.
 * He created the magical prison Demonreach by building it once, at five different times, all at the same time. And he put in place a Failsafe: a fire that would kill them rather than release them.
 * Donar Vadderung told Harry that the Failsafe was called: "Banefire".

in the series

 * Ebenezar McCoy has Merlin's journals among the journals of all of his mentor's predeceasing him.


 * Ebenezar McCoy tells Harry Dresden that Merlin was taught by Donar Vadderung.