He took on a king of the jungle (3)
I believe the answer is:
ali
'he' is the definition.
'took on a king of the jungle' is the wordplay.
I cannot quite understand how this works, but
'a' is within the answer.
The remaining letters 'li' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ali that I've seen before include "Mohammad . . ., . . . Hewson" , "Muhammad or Baba?" , ""The Greatest" boxer" , "Lepidopterous floater, apian stinger, d. 2016" , "Son-in-law to Muhammad" .)