Mary Wilson perhaps unsurpassed (7)
I believe the answer is:
supreme
I believe this is a double definition.
'mary wilson' is the first definition.
(Mary Wilson was a member of the band The Supremes)
'unsurpassed' is the second definition.
(I've seen this before)
'perhaps' is the link.
(Other definitions for supreme that I've seen before include "Most excellent" , "Ranked highest" , "Highest in rank - incomparable" , "God" , "Unrivalled" .)