His code of laws took a lot of executing (5)
I believe the answer is:
draco
'his code of laws took a lot of executing' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'his code of' is the wordplay.
'his code' becomes 'drac' (I can't explain this - if you can you should give a lot more credence to this answer).
'of' becomes 'o''.
'drac'+'o'='DRACO'
Can you help me to learn more?
(Other definitions for draco that I've seen before include "archon" , "seen among the stars" , "Athenian statesman" , "Harsh legislator" , "group of stars" .)