The common ancestor of humans, chimpanzees and gorillas was a generic ape that lived either in east africa or in southern europe. One good candidate is Nakalipithecus, an ape who lived 9.8 million years ago in Kenya. Another very similar looking ape Samburupithecus which was also found quote close by. The fact is not that we do not have a candidate for common ancestor. Rather there are quite a lot of similar looking fossils, each close kin of the others, and each of which are good enough candidates to be common ancestors. One of them is, but bones alone are insufficient to definitely say this one is the common ancestor and that one is not. The situation is, as I said, you cannot distinguish between your great great grandfather and your great great granduncle by bones alone. But one of them will be your paternal ancestor, certainly.
Nakalipithecus - Wikipedia
I will also make certain points.
1) The difference between species boils down to difference in DNA letters
2) We know how much difference in DNA letters exist between chimpanzees and humans
3) We know at what rates the DNA letters change by mutation from one generation to the next. The mutation rate.
4) We know speciation happens. We have seen it in insects, fishes, birds etc. multiple times now. The mechanisms of speciation are well know and well evidenced. So is the mechanism of mutation and natural selection that drives evolutionary alteration.
5) We know that 8-9 million years is more than enough time to account for all DNA changes we see between humans and chimpanzees
6) We see from the structure of how the DNA letters are arranged with additions, deletions and insertions...that the DNA of humans and chimpanzees came from a common initial source. This is very similar to how we trace ancestry of language. We can see from the words, grammar etc. that American English emerged from early modern British English and so on.
7) We have several candidate fossil apes with the kind of features we expect of this common ancestor.
8) We have hundreds of later transitional fossil hominids that chart out the evolution of modern humans from this early common ancestor. (Sahelanthropus, Ororin, Ardipithecus, Australopithecus- gracile and robust, Homo habilis, Homo ergaster, Homo erectus, Homo heidelbergensis, Neanderthals, Humans etc. etc.) Hundreds of species. Thousands of specimens. Spanning over these 8 million years. More are discovered every year. Evolutionary trajectory is non-linear and tree like with many branches and sub-branches...as predicted by Darwin.
So as far as science is considered, the fact of evolution of humans from ancestral stock of apes is as well established as the fact the earth is spherical. To believe or not is upto you.