Ruffalo's early advocacy emerged in the late 1990s, coinciding with growing public awareness of climate change and social justice. His involvement with environmental groups like the Natural Resources Defense Council (NRDC) marked a pivotal shift from entertainment to activism.
By the mid-2000s, Ruffalo's public stance on issues such as renewable energy and disaster relief solidified his role as a prominent voice in humanitarian discourse, influenced by the post-9/11 era's emphasis on global solidarity.