In Episode 3, players are given a quiz by Keroshane in order to determine what type of companion they will start out with. Corkos are one of three starting companions, the other two being Becola and Sabali.
This companion is inspired by Dobhar-chú, a mythological animal.
Its name is an anagram of "croko".
It seems to be the mixture of several animals (crocodile, fish, snake, duck, cat, dog).