Social Security Act
  
Social Security's very name captured best the core principle of the New Deal at full flood: the idea that the government could and should provide a social safety net to protect individual citizens from the uncertainties of the free market. The same free market that just decided to collapse on everyone.
Social Security's best known today as a retirement plan, but it also provided unemployment insurance and welfare for fatherless children and their mothers. Prior to the passage of the Social Security Act, a large majority of Americans worked until the day they died. The notion of "retirement" was foreign to all but the wealthiest elite.
Prior to the passage of the Social Security Act, almost all Americans who suffered sudden economic calamity—the loss of a job, or the death or abandonment of a family's chief breadwinner—would soon find themselves homeless and starving. Social Security helped millions of Americans step back from the precipice of economic ruin.
Still today one of the most popular government programs ever instituted, Social Security forever changed the relationship between the free market, the American people, and our government.