Connoisseur welcomes popular investor (9)
I believe the answer is:
financier
'investor' is the definition.
(I've seen this before)
'connoisseur welcomes popular' is the wordplay.
'connoisseur' becomes 'fancier' (I've seen this before).
'welcomes' indicates putting letters inside (in sense of 'invites in').
'popular' becomes 'in'.
'fancier' enclosing 'in' is 'FINANCIER'.
(Other definitions for financier that I've seen before include "Money manager" , "One dealing in big money" , "Manager of large-scale monetary resources" , "One handling money" , "Person engaged in large money transactions" .)