[DougHaber]

According to Wikipedia:

  Udo of Aachen (c.1200–1270) is a fictional monk, a 
  creation of British technical writer
  Ray Girvan, who introduced him in an April Fool's hoax
  article in 1999. According to the article, Udo was an
  illustrator and theologian who discovered the Mandelbrot
  set some 700 years before Benoît Mandelbrot.

  Additional details of the hoax include the rediscovery of
  Udo's works by the also-fictional Bob Schipke, a Harvard
  mathematician, who supposedly saw a picture of the
  Mandelbrot set in an illumination for a 13th-century carol.
  Girvan also attributed Udo as a mystic and poet whose
  poetry was set to music by Carl Orff with the haunting O
  Fortuna in Carmina Burana.

https://en.wikipedia.org/wiki/Udo_of_Aachen

[krylon]

I have to admit I am a little sad this was an April fools joke. It would have been so cool if some obscure medieval monk had discovered the Mandelbrot set centuries ago.

Then again, IIRC, complex numbers were not invented (discovered?) until the 1500s, so good old Udo would have had a hard time figuring out the math.

[donquichotte]

He "did" invent complex numbers! From TFA:

"Initially, Udo's aim was to devise a method for determining who would reach heaven. He assumed each person's soul was composed of independent parts he called "profanus" (profane) and "animi" (spiritual), and represented these parts by a pair of numbers. Then he devised rules for drawing and manipulating these number pairs. In effect, he devised the rules for complex arithmetic, the spiritual and profane parts corresponding to the real and imaginary numbers of modern mathematics."

[krylon]

Serves me right for not reading the "article" thoroughly. ;-)