The activist known for strongly opposing child labor in factories was Lewis Hine. A photographer and sociologist, Hine dedicated his life to documenting the harsh conditions faced by child laborers in the early 20th century America. His haunting images showcased children working long hours in dangerous environments, effectively bringing the issue to public attention. Through his photographs, he aimed to spur social reform, advocating for child labor laws and an end to exploitative labor practices. Hine's work played a vital role in raising awareness and fostering a movement towards better protections for children.