Regan's father (4)
I believe the answer is:
lear
'regan's father' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lear that I've seen before include "Tragic Shakespeare king - quite real" , "Tragic character" , "British king in play" , "Mad king" , "Edward, writer of nonsense verse" .)