Actor finally plays Robert Wadlow? (8)
I believe the answer is:
stallone
'actor' is the definition.
Both the definition and answer are singular nouns.
Maybe you can see an association between them that I can't see?
'finally plays robert wadlow?' is the wordplay.
'finally' indicates one should take the final letters.
'wadlow?' becomes 'allone' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The final letters of 'plays robert' are 'st'.
'st'+'allone'='STALLONE'
Can you help me to learn more?
(Other definitions for stallone that I've seen before include "Hollywood actor" , "Sylvester ........, Hollywood tough guy" , "Sylvester ..., cinema's Rocky" , "See 6" , "Sylvester - (Rambo)" .)