The one-legged captain makes a habit of it (4)
I believe the answer is:
ahab
'the one-legged captain' is the definition.
'Ahab' can be an answer for 'captain' (Captain Ahab appears in Moby-Dick). I'm not certain of the 'the one-legged' bit.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ahab that I've seen before include "Melville's whale chaser" , "Fictional whaler" , "sea captain" , "Jezebel's husband - Moby Dick's hunter" , "Israelite king" .)