So I found something interesting...
In the Underworld story, The Beast mentions the Clairvoyant's brother, named "John Dee". Sparton said that said The Alchemist was based on "Dr. Dee"; Dr. Dee being actual dude in the 16th Century, he was a profound mathematician and studier of alchemy and magic. His full name? John Dee. https://en.wikipedia.org/wiki/John_Dee
(NF nailed the design, in terms of likeness to Dr. Dee)
TL;DR: It's the Clairvoyant's brother.