Dog, company ultimately for soldier (5)
I believe the answer is:
corgi
'dog' is the definition.
(I know that corgi is a type of dog)
'company ultimately for soldier' is the wordplay.
'company' becomes 'co' (abbreviation).
'ultimately' suggests the final letters.
'soldier' becomes 'GI' (GI can mean a US soldier).
The last letter of 'for' is 'r'.
'co'+'r'+'gi'='CORGI'
(Other definitions for corgi that I've seen before include "man's best friend" , "found in the kennels" , "Welsh breen of dog" , "Cardigan, possibly" , "Royal canine" .)