American researcher Dian Fossey and her book "Gorillas' in the Mist" first brought international attention to the primates' plight. The mountain gorilla population dropped sharply in the last century because of poaching, illness and human encroachment, but their numbers are now rising - a hopeful sign for the critically endangered species.
These days, an estimated 900 mountain gorillas live in the steep-sloped forests of Rwanda and neighboring Congo and Uganda, the last of their species on earth.
In Rwanda, a country that has struggled with the ravages of genocide and civil war, conservation tourism is big business - seen as key to the welfare of the gorillas as well as Rwanda's economy.
In this photo, a male silverback from the Amahoro family sits in the dense forest on the slopes of Mount Bisoke volcano in Volcanoes National Park, northern Rwanda, September 4, 2015.