Scientist, one shrouded in smoke (5)
I believe the answer is:
curie
'scientist' is the definition.
(I've seen this before)
'one shrouded in smoke' is the wordplay.
'one' becomes 'i' (Roman numeral).
'shrouded in' indicates putting letters inside.
'smoke' becomes 'cure' (I've seen this in other clues).
'i' inserted within 'cure' is 'CURIE'.
(Other definitions for curie that I've seen before include "measure of radioactivity" , "Unit of radioactivity" , "Marie --, discoverer of Radium" , "Marie -, Fr. physicist" , "Scientist" .)