The influential social reformer known for their fight against child labor is Lewis Hine. A photographer and sociologist, Hine documented the harsh realities of child labor in the early 20th century through powerful images that raised public awareness. His work played a pivotal role in the eventual passage of child labor laws in the United States. Hine's compelling visual narratives highlighted the urgent need for reform and have continued to influence discussions on children's rights and labor protections.