Ultimately grim animal molested USPS worker (7)
I believe the answer is:
mailman
'worker' is the definition.
(mailman is a kind of worker)
'ultimately grim animal molested' is the wordplay.
'ultimately' says to take the final letters.
'molested' indicates an anagram.
The final letter of 'grim' is 'm'.
'animal' anagrammed gives 'ailman'.
'm'+'ailman'='MAILMAN'
'usps' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for mailman that I've seen before include "He delivers the post in the US" , "American man of letters" .)