Paracelsus ..at least if we go by the following portrait anyway.
This is a copy of a lost portrait by Quentin Matsys and shows him with red hair, ruddy cheeks and what looks like some red animal fur on an even redder hat.
Paracelsus, of course, was a famous physician, botanist, alchemist, astrologer and all round general smart arse.
I should thank Barry for this one (the author of the All About Redheads article I linked to in an earlier post) He shared it on his Facebook page and I promptly stole it.
Whilst checking out Paracelsus I also came across this guy. Another red-haired physician, this one being the 17th century medical man Thomas Willis. He apparently had dark red hair and a stammer. I found this picture of him;
And also this image from a book he had published in 1663, which I can't resist sharing for its sheer bizarreness.