There is a long history of debate over the existence of an alleged gorilla-like chimpanzee, known as the kooloo-kamba (an onomatopoeic reference to its call).
As recently as the late 1960s, primatologist W. C. Osman Hill regarded the kooloo-kamba as a distinctive chimp subspecies thought to inhabit Cameroon, Gabon and the former French Congo, and to live alongside chimps of the nominate subspecies.
Previous researchers regarded it as a distinct species somehow intermediate between chimps and gorillas, or the product of gorilla-chimp hybridization.
Supposedly, several such individuals were kept in captivity during the late 1800s and ealy 1900s, including ‘Mafuca’ of the Dresden Zoological Garden, and ‘Johanna’ of Barnum and Bailey’s circus collection.
It now seems that the kooloo-kambas of the older literature reflect the fact that both gorillas and (especially) chimps are more variable in facial anatomy, body size and overall appearance than many primatologists were once willing to accept. Chimps of some populations are larger, darker-skinned and superficially more ‘gorilla-like’ than many of the chimps first brought back to Europe, but this doesn’t mean that such animals are hybrids, or intermediates.
Various other controversial African apes–most notably the Pygmy gorilla Pseudogorilla mayéma lauded by cryptozoologist Bernard Heuvelmans–also tell us more about our poor understanding of variation, and don’t necessarily point to the presence of additional distinct species.