Well, several kinds of monkeys were well-known in ancient times. Here is an Egyptian relief from the temple of Medinet Habu from around 1150 BC for example, which features a congress of baboons joining Ramses III. in worship. And Barbary macaques lived in many places in North Africa and still are all the way up in Gibraltar.

There is loads of descriptions from Roman authors of "apes" (simii) being held as pets or for entertainment. And since it's the Romans they threw zoophilia in the mix as well, a mime, which is essentially uncensored Roman scetch comedy, by Decimus Laberius (this one, down in line 55) jokes about a pharmacist falling in love with an ape (farmacopoles simium deamare coepit), at least if you don't want to go with the interpretation that "simium" refers to a man in some sort.

Anyway, great apes.
Great apes weren't really discovered or at least decisively described until the 1600s, when primarily the Dutch explorers went around Africa and Asia, where some would return with strange human-like skeletons of beasts they had killed. Occasionally they would even manage to get a live infant back to Europe, which caused quite the sensation understandably, although it wouldn't last long since nobody really had any idea on how to treat them properly and they soon died from disease or other causes.

The Observationes Medicae of Dutch surgeon Nicolaes Tulp (protagonist of Rembrandt's famous The Anatomy Lesson of Dr. Nicolaes Tulp, 1632) published in 1641 describe a creature brought back with a Dutch East India Company vessel that he called "orang-outang" or "Indian Satyr". It was actually a chimpanzee but anyway, it is now generally considered to be the first natural description and drawing of the species. That book even got a second edition in 1652, which was most unusual for such a book in that time, but not that crazy when you consider that his drawing of that strange new human-like creature spread like the black death and inspired all sorts of discussions on human origins.

The first description of an actual orangutan seems to lie with another Dutch living in Jakarta, named Jacob de Bondt (1599-1631), in his 1658 posthumously released Historiae naturalis et medicae Indiae orientalis libri VI. They actually acquired a rather positive image in scientific circles as docile intellectuals, many marvelled at their tool use and social abilities and their development of a dramatically different appearance in adulthood.

I don't know about individual reaction though but you could probably come up with some sort of correspondence or Dutch East Indies log if you knew where to look.