Oliver was a young chimpanzee, likely kidnapped from the Congo at an early age, and sold to animal trainers in 1970. Frank and Janet Berger noticed as the chimp aged that he had very human-like traits, such as walking upright and having features that resembled an old man. Oliver was trained by the Bergers for 7 years, when another peculiar trait made itself known to the pair of trainers.
Oliver seemed to be attracted to Janet, much more so than any of the female apes which were also kept by the Bergers. To her displeasure, Oliver may have tried to mate with her. This was the end of the road for Oliver with the Bergers, and they sold him to a lawyer named Michael Miller.