Final answer:
Carnegie and Rockefeller were known for their philanthropic efforts during their older years, having established significant foundations and contributed to various social causes, inspired by notions of social responsibility and social Darwinism.
Step-by-step explanation:
Andrew Carnegie and John D. Rockefeller were both significant figures during America's Industrial Age and were known for their vast business empires in steel and oil, respectively. During their old age, rather than competing in business, they became well-known for their efforts in philanthropy. Carnegie, who came from a humble background, ardently believed in giving back to society and did so through funding of libraries and educational institutions. He espoused this viewpoint in his work "The Gospel of Wealth." Rockefeller, on the other hand, also became a prominent philanthropist, although his business practices prior were often criticized for being predatory. Nonetheless, both men engaged in giving their wealth to numerous causes, partially influenced by the social Darwinism ideas prevalent at the time, indicating the wealthy's responsibility towards the less fortunate.