Chess champ Spassky (5)
I believe the answer is:
boris
'chess champ spassky' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for boris that I've seen before include "Pasternak, perhaps" , "- Johnson, Mayor of London" , "Leading Brexiteer's given name" , "- Godunov, Russian tsar" , "- Pasternak, Russian author (Doctor Zhivago)" .)