Gorrillas can weigh up to 600 pounds. Gorillas are known for their enormous physical strength. Despite their giant, strong bodies and scary appearance, gorillas are rather gentle Apes and don't normally harm other species unless they are very angry or in self-defense, and they are herbivores.
Young gorillas all have black backs and the backs of female gorillas stay black all their lives. By contrast male gorillas start to get silver hair on their backs when they mature, at about 12 years of age, adult males are called silverbacks. Silver hair on their backs show male gorillas have reached the prime of life. Silverbacks have their full adult strength or will soon reach adult strength.
Comparison with human hair
This is similar to the way that the hair on human heads gets grey with age. Of course human hair gets grey much later in life, when we are middle aged or old and in humans both sexes get grey hair. In humans grey hair indicates people are passed the prime of life and no longer as strong as they used to be. (Grey hair in a human doesn't indicate strength but indicates age and experience. Life experience counts for something in our society and counts for more in traditional societies. So in traditional societies grey hair can be a mark of dominance as it is among gorillas.)
Types of gorilla
There are two types of gorilla: the lowland gorilla and the mountain gorilla. Their names pretty much give away where their habitats are. Both gorilla types live in Africa, like their other primate family members. They make nests to sleep in but rarely use a nest more than one night.
Gorillas together with Chimps and Orangs split from the gibbons and siamangs 20 Million years ago. Gorillas are more closely related to chimps than they are to any other animal. Humans are also more closely related to chimps than they are to any other animal. 
Gorillas are also the third smartest living primates.  A domesticated gorilla named Koko knows over 200 words in sign language.