One who operates in theatre, not needing screen (5,5)

'one who operates' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'theatre not needing screen' is the wordplay.
I cannot quite see how this works, but
'theatre' could be 'stage' (stage is a kind of theatre) and 'stage' is found in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is found in the answer.
This explanation may well be incorrect...

'in' acts as a link.

Can you help me to learn more?