When did Europeans learn about the African great apes?

Can anyone tell me when European explorers first learned about chimpanzees and gorillas? What was their initial reaction? Did they think the apes were extremely primitive humans, or just vaguely humanlike animals (=animals in the everyday colloquial sense of “not human”)?

The first actual specimens of the gorilla were obtained in Gabon by the French-American explorer Paul du Chaillu in the mid-1850s. His accounts of their behavior were widely disbelieved at the time. Although told in a melodramatic style and somewhat exaggerated, much of his description turned out to be accurate.

Rumors and tales of large apes go back much further, to classical times, I believe.

From here:

Note that the original name given to the chimpanzee, Homo sylvestris, “man of the forest,” implies a recognition of a close affinity with humans. Also the identification with the “pygmies” of classical literature imples the same.

I believe European knowledge of chimps at least goes back further than the 1600s.

Chimpanzees seem to have been known at least through travelers’ tales to the Greeks and Romans.

From here:

Aside from the bit about having the hindquarters of a donkey, that seems to be the description of a chimp, especially the part about using the hands in running

Might the “dog-headed” reference, the “ashen colour” and the bit about having the hindquarters of a donkey have been about baboons rather than chimpanzees? Hamadryad baboons were sacred in ancient Egypt, so they would have been known to the Greeks. I agree that the “man-like face” in Pythagoras’ account sounds more like a chimp though.

I thought this could very well be a description of a gorilla.
They match the color perfectly and their backs do not look too humanoid.
A gorilla does not look very much like a donkey on the backside but at least it’s closer than a chimp.

The residents of Hartlepool, UK were, seemingly, not aware of the existence of monkeys during the Napoleonic war. This makes for great fun in the football chanting community!

The Hartlepool Monkey Hangers

References to cynocephali, or dog-headed men, may well be based in baboons. However, as you say the description of the “onokentauri” specifies that the face is that of a man. That the animal makes use of its hands in running only when speed is necessary also implies a chimp, since baboons are quadrupedal even when walking. On the other hand, the reference to thick hair about the face and to swelling teats are more like a hamadryad baboon. Of course, since these reports are based on hearsay anyway, it’s quite possible that they confuse and combine the traits of several different animals, so it may not be possible to identify a definitive source.

I doubt the account of the onokentauri refers to a gorilla, because first of all they are much less widespread than chimps and less likely to have become known to the Greeks, and second I think that any fanciful account would be very likely to include reference to their great size.

Further to Colibri’s mention of him, one of the essays in Stephen Jay Gould’s The Flamingo’s Smile discusses Tyson’s The Anatomy of a Pygmie in some detail, arguing that as a believer in the Great Chain of Being he overemphasised the closeness of chimps and humans.