Bernie was pet of Agent 51.
Bernie was Agent 51's pet hamster, and the two had a lot of fun times together. However, when Bernie died, 51 missed him very much and became somewhat bitter.
Bernie's ghost watched 51 break down about him, while he notes that he got it over it.
When Bernie was alive, he had brown and white fur.
Bernie seems to be very loyal to his master, even in death. Like 51, he was sad about being separated from but he remarked to the pets that even he got over while as a ghost.