Artemis turned him into a stag (7)
I believe the answer is:
actaeon
'artemis turned him into a stag' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for actaeon that I've seen before include "Old Greek hunter" , "Hunter changed into a stag" , "Artemis changed him to a stag; at once a (anag.)" , "Hunter who transformed" , "Hunter who was turned into a stag" .)