Will's false friend I back (4)

I believe the answer is:

iago

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

'will's false friend' is the definition.
I can't tell whether this definition defines the answer.

'i back' is the wordplay.
'back' becomes 'ago' ('years back' means 'years ago').
'i'+'ago'='IAGO'

Can you help me to learn more?

(Other definitions for iago that I've seen before include "The villain who tricked Othello" , "Othello's treacherous officer" , "Othello's Ancient" , "Othello's enemy" , "Shakespeare's jealous villain" .)

I've seen this clue in the Sydney Morning Herald.

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