A man called Gareth hides (5)
I believe the answer is:
edgar
'a man' is the definition.
'called gareth hides' is the wordplay.
'hides' indicates a hidden word.
'EDGAR' can be found hidden inside 'called gareth'.
(Other definitions for edgar that I've seen before include "Part of 1 25 [KING LEAR]" , "Grade (anag)" , ". . . . . Allan Poe, master of the macabre" , "J. -- Hoover, FBI boss" , "Great writer of spooky stories, . . . . . Allan Poe" .)