Jacob Riis was a Danish-American journalist and social reformer who is best known for his photographs and writings about the conditions of the poor and immigrant communities in New York City in the late 19th century. He was born in Denmark in 1849 and immigrated to the United States in 1870.

In the early 1880s, Riis began working as a police reporter for the New York Tribune, where he gained access to the city's tenements, slums, and other areas where poor and immigrant communities lived. He was shocked by the squalor and poverty he saw, and he began using his camera to document the conditions. His photographs, which were often accompanied by his own writings, provided a powerful and often-heartbreaking look at the lives of the city's most marginalized residents.

In 1890, Riis published his most famous book, "How the Other Half Lives: Studies Among the Tenements of New York." The book was a bestseller and brought the issue of poverty and urban life to the forefront of public consciousness. Riis's work helped spur the development of new housing and health codes, as well as the creation of the New York City Police Department's first juvenile bureau.

Riis also wrote several other books, and he remained an influential figure in the early years of the progressive movement. He died in 1914 but his work still remembered as a powerful record of the living conditions of the poor and immigrants in the late 19th century New York City.