My personal recommendation.
I would like to put forward Professor Hugh Davson. In the post war period he did ground breaking work on the physiology of the brain, ophthalmic research (leading to the setting up of several Corneal Banks), and other important medical work regarding the Blood/Brain Barrier. Although not IT related, and therefor probably not high on any list produced here, I knew the man and respect him. Most of his work was conducted at the Institute of Ophthalmology on Judd Street, University College on Gower Street, University of Louisville on South Seventh Street, and California Institute of Technology on Wilshire Boulevard.