Ranko is a gorilla kept the Craig Dhui Castle by Dr. J.W. Müller in order to deter strangers from visiting and possibly discovering his counterfitting operations.
History
The Black Island
Ranko attacks Tintin when he arrived on the Black Island and his arm is eventually broken after a conflict between the two. He is terrified of Snowy, although possessing tremendous strength. It turns out that he is in reality harmless, follows Tintin to shore without harming him. Tintin helps his arm and placed Ranko in a Glasgow zoo after the arrest of his keepers.