I learned about Oliver the chimpanzee after answering another question and I developed a kind of sympathy towards his story.
The abstract of my answer is that Oliver was a common chimpanzee that had retained some juvenile characteristics in his face that made him appear more 'human-like' and a preference for walking upright that he could have developed as a juvenile growing with his first owners, a couple that bought him when he was about two y.o. The most peculiar trait he shoed was how upright he could walk, but this type -although very excepcional- of gait has been found in some other apes like the gorilla of the video I have added. And finally, some years of abuse resulted in muscle atrophy and loss of all teeth wich contributed to making his appeareance more slender and his face more plane.
Oliver was famed as a chimpanzee with many human like traits, but in fact many studies carried out after his death showed clearly that he was a common chimpanzee without chromosomic anomalies.
Afrom the examined Oliver's in 1996 and revealed that Oliver had forty-eight chromosomes instead of forty-seven. This disproved the earlier claim that he did not have a normal chromosome count for a chimpanzee.Oliver's cranial morphology, ear shape, freckles and baldness fall within the range of variability exhibited by the Common Chimpanzee.Scientists performed further studies with Oliver, the results of which were published in the American Journal of Physical Anthropology.However a full DNA test has never been performed. Although many requests were made for access to Oliver for medical testing during his later years at Primarily Primates and again after his death in 2012, it was the policy of PP to refuse all such requests, calling those inquiries "scientific tourism."
Judging by the pictures I have seen he looked like if he had retained some juvenile characters like a somehow flatter face (aslthough that the effect was stressed by the fact that many of the photographs were taken when he was old and had his teeth removed), bald and without beard. He also had a tendence for walking upright, strinkingly upright, and rarely was seen knucling. He was a well developed male in spite of the juvenile traits in his appeareance. Also, reading his biography -it is very interesting- it results that Oliver was purchased by a Pensilvannia laboratory when he was about 30 years old, and that he spent nine years in a small cage what resulted in his muscles atrophying, which could give him the slender look he exhibits in the pics, apart from horrible mental and phisycal suffering. Oliver, with all his fame, was an abused chimp, and I congratulate that people of Primarly Primates finally took care of him and decided to maintain scientific analysis far from him for the rest of his life:
Oliver was purchased in 1989 by the Buckshire Corporation, a Pennsylvania laboratory leasing out animals for scientific and cosmetic testing. His entrance examination revealed some previous rough handling. He was never used in experiments, but for the next nine years, his home was a small cage, whose restricted size resulted into the point that Oliver's limbs trembled.In 1996, Sharon Hursh, president of the Buckshire Corporation, after being petitioned by, allowed his retirement to Buckshire's colony of 13 chimpanzees.
So, accordingly to the studies carried out, and in absence of a genetic study, it seems that Oliver was a common chimpanzee whose 'human-like' traits had been highly hyped by his owners who had exhibited him.
The peculiar -for a chimp- way of walking is also not unheared of in some few other non human apes (very few), like the gorilla of this video: