All right, a Greek character follows the animal (5)
I believe the answer is:
Here is my best explanation:
'the animal' is the definition.
(I've seen this before)
'all right a greek character follows' is the wordplay.
'all right' becomes 'ok' ('ok' can be a synonym of 'all right').
'greek character' becomes 'pi' (letter from the Greek alphabet).
'follows' says to put letters next to each other.
(Other definitions for okapi that I've seen before include "Giraffe family member", "Mammal related to the giraffe", "African ruminant", "rainforest ruminant", "One of the giraffe family", "Small giraffe", "Hoofed mammal", "Animal related to giraffe", "african" and "Central African animal".)