wikipedia summarizes like this:
Caspar David Friedrich was born on September 5, 1774, in Greifswald, Swedish Pomerania, on the Baltic coast of Germany. The sixth of ten children, he was brought up in the strict Lutheran creed of his father Adolf Gottlieb Friedrich, a candle-maker and soap boiler. Records of the family's financial circumstances are contradictory; while some sources indicate the children were privately tutored, others record that they were raised in relative poverty. Caspar David was familiar with death from an early age. His mother, Sophie Dorothea Bechly, died in 1781 when he was just seven. A year later, his sister Elisabeth died, while a second sister, Maria, succumbed to typhus in 1791. Arguably the greatest tragedy of his childhood was the 1787 death of his brother Johann Christoffer: at the age of thirteen, Caspar David witnessed his younger brother fall through the ice of a frozen lake and drown. Some accounts suggest that Johann Christoffer perished while trying to rescue Caspar David, who was also in danger on the ice.In our safe world parents who lose children and children who lose their parents say that these are awful, life-changing events, and that afterwards things are never the same; how did it change society when most people had such experiences? (Monk by the Sea, 1808-1810)
The artist should paint not only what he sees before him, but also what he sees within him. If, however, he sees nothing within him, then he should also refrain from painting that which he sees before him. Otherwise, his pictures will be like those folding screens behind which one expects to find only the sick or the dead.Temple of Juno in Agrigento, 1828-1830.
I am not so weak as to submit to the demands of the age when they go against my convictions. I spin a cocoon around myself; let others do the same. I shall leave it to time to show what will come of it: a brilliant butterfly or maggot.Above, Two Men by the Sea, 1817; below, Man and Woman Contemplating the Moon, 1820.