Ring Ryan? A final letter? (5)

I believe the answer is:

omega

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

'final letter?' is the definition.
(I've seen this before)

'ring ryan? a' is the wordplay.
'ring' becomes 'o'.
'ryan?' becomes 'meg' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'o'+'meg'+'a'='OMEGA'

Can you help me to learn more?

(Other definitions for omega that I've seen before include "Final outcome" , "Ultimate letter" , "Foreign character" , ""The Alpha and the ___"" , "character from Athens" .)

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

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