Actor one’s seen in The Bridge (8)
I believe the answer is:
thespian
'actor' is the definition.
(I know that actor can be written as thespian)
'one's seen in the bridge' is the wordplay.
'one' becomes 'i' (Roman numeral).
'seen in' is an insertion indicator.
'bridge' becomes 'span' (synonyms).
'the'+'span'='thespan'
'i' going into 'thespan' is 'THESPIAN'.
(Other definitions for thespian that I've seen before include "Actor; relating to drama" , "Stage-player" , "person in the acting business" , "stage performer" , "Dramatic performer" .)