Worker in Salvation Army who brings you presents? (5)
I believe the answer is:
santa
'who brings you presents?' is the definition.
(Santa Claus)
'worker in salvation army' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'in' is an insertion indicator.
'salvation army' becomes 'SA' (abbreviation).
'ant' going into 'sa' is 'SANTA'.
(Other definitions for santa that I've seen before include "generous figure" , "He comes down chimney" , "St Nicholas" , "bringer of gifts" , "Dec's visitor?" .)