Merlin

From Stormravengaming

Let us examine these earlier magicians that Portishead makes so much of... Merlin was another but, as he was upon his mother's side Welsh and upon his father's Infernal, he will scarcely do for that pattern of respectable English Magic upon which Portishead, Norrell and Strange have set their hearts.

— Jonathan Strange, Jonathan Strange and Mr Norrell

A great wizard of the Realm, Merlin also traveled to many other planes of existence. His adventures on the mundane plane have given rise to many different legends there. Presto once sought to serve as an apprentice to (the long-dead) Merlin, which perhaps led eventually to his ability to master the archmage's floating island.