1984
Grimdark has always been a concept of humanity living in the worst environment as possible, and there is not even a single joy can be found in grimdark. 1984 is such example of grimdark. It is a novel by George Orwell published in 1949. It is primary about what happen if the government has the complete control of everyone, where you will be watched everyday and being forced to do what the government said, or else you'll be vaporised. This book is basically the inspiration to all grimdark, including warhammer 40k.
Plot
A guy name Winston wasn't happy about his life. He is sick of doing the same thing, exhausting at work and not having enough to eat. But his life changed when he met Julia, who gives him what he want, which is something the party is unacceptable with. Winston had a fun time fucking Julia, learning about the past and eating the real food from the party, until he was caught by the thought police and was sent to brainwashed. O'brien, who is Winston's boss, also existed in his childhood, is actually an agent from the party, and he tortured Winston, then sent him to room 101 to meet his fear. In the end, Winston returned to normal and believes 2+2=5.