Crossword Genius

In part, he'll do (5)

Ross

I believe the answer is:

actor

I'm a little stuck... Click here to teach me more about this clue!

'in part' is the definition.
'actor' can be an answer for 'part' (thesaurus). I am not certain of the 'in' bit.

'he'll do' is the wordplay.
I cannot quite see how this works, but
'do' could be 'act' (I've seen this before) and 'act' is present in the answer.
The remaining letters 'or' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for actor that I've seen before include "Person performing on stage or screen" , "One in a play" , "For example, Colman" , "Theatrical performer" , "Stage-player" .)

I've seen this clue in the Evening Standard.
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