The American politician instrumental in establishing social security was Franklin D. Roosevelt. During his presidency, he introduced the Social Security Act of 1935, aimed at providing financial support to the elderly, unemployed, and disabled. This landmark legislation represented a shift towards a more welfare-oriented approach to governance, marking a significant expansion of the federal government’s role in citizens' lives. Roosevelt's vision of a safety net aimed to protect Americans during economic hardships and foster a more equitable society, with social security programs becoming vital for millions over the decades.