Vitamin C or L-ascorbate is an essential nutrient for a large number of higher primate species, a small number of other mammalian species (notably guinea pigs and bats), a few species of birds, and some fish. 
The presence of ascorbate is required for a range of essential metabolic reactions in all animals and plants. It is made internally by almost all organisms, humans being the most well-known exception. It is widely known as the vitamin whose deficiency causes scurvy in humans. It is also widely used as a food additive.