His depredations affect the stockholder (7)
I believe the answer is:
rustler
This clue could be a double definition.
'his depredations affect' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'stockholder' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'the' acts as a link.
Can you help me to learn more?
(Other definitions for rustler that I've seen before include "Cattle-thief" , "Stock taker?" , "Cattle stealer" , "one whose stock-taking is dishonest" , "person taking stock" .)