Final answer:
Jacob A. Riis was the reformer and photographer who documented the living conditions of the urban poor in New York City's tenements in the late 1800s, impacting social reform and legislation.
Step-by-step explanation:
In the late 1800s, Jacob A. Riis photographed tenement buildings in which the urban poor lived. His impactful work played a role in catalyzing social reform.
Jacob A. Riis was a social reformer and photographer known for his work documenting the living conditions of the urban poor in New York City during the late 19th century. Through his powerful images and writing, particularly in his book How the Other Half Lives, Riis exposed the dire state of tenement housing and the effects of poverty strangling the lower classes. His photojournalism shone a light on the cramped, unsafe, and unsanitary conditions in which many immigrant families lived, invoking public and legislative action to address these inhumane living situations. Riis's photographs, such as those taken in Mulberry Street, revealed the cramped quarters, lack of light and air, and general misery that characterized tenement life. His advocacy and images directly influenced public perception and legislation, leading to significant improvements in housing standards for the poorest residents of New York. Riis's work is recognized not just for its immediate impact but also its significance in the history of documentary photography and social reform.