In his 2001 volume "Wonders of Numbers," Clifford Pickover ranked the "5 Strangest Mathematicians Who Ever Lived." One could offer a lot of suggestions and debate on this subject, but here is Pickover's slate, with links to their Wikipedia pages:
1. Paul Erdos
2. Srinivasa Ramanujan
4. Theodore Kaczynski
5. John Nash
(I'll throw in a couple more that quickly come to mind: Grigori Perelman and Alexander Grothendieck.)
The oddest member in this whole group, from my viewpoint, is Kaczynski, who in case you've forgotten or didn't know, was a loner, domestic terrorist also known as the "Unabomber" (and also a Harvard grad and Michigan math PhD.) who eluded law enforcement for over 17 years, living a spartan, reclusive life in rural Montana, while sending out his occasional mail bombs and manifestos.