Cleveland, arguably, was one; Lee Jackson came later (6)
I believe the answer is:
python
'cleveland' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for python that I've seen before include "Large non-venomous snake" , "Large snake that crushes and swallows its prey" , "Heavy-bodied snake" , "Snake that kills its prey by squeezing" , "Tropical non-venomous snake" .)