In the field of computing, I think the greatest contribution to the world vs least fame & fortune goes to the inventor of the World Wide Web.
It's sad that outside of the computing world, Tim Berners-Lee is unknown. Asking your dentist, aunt, or barber about who they think invented the web leads to some amusing replies.
I've actually done this and after telling them about Berners-Lee, I found the following themes to be common:
(1) Incredulousness that it was one person. People either think it had to be a big company or that it somehow "evolved" into existence (you know, the way television or photography just kind of happened without any particular persons being involved /irony).
(2) Belief that he chose to not accept the money. That is, he could have made a fortune if he wanted to, but for unspecified reasons he didn't want the money. I've tried to explain that the web wouldn't have succeeded if he tried to charge for it (even assuming that CERN let him charge for it), but there's a popular belief that great work always gets rewarded unless one explicitly opts out of the reward.
AN ASIDE: I think that in all human endeavor, the record for greatest contribution to the world vs least fame & fortune, where the inventor is truly known, should go to Cai Lun (also spelt Ts'ai Lun), the inventor of paper. He's a real person and historically well-documented as the actual inventor of paper: