'The Untouchables' were a group of nine U.S. federal law-enforcement agents led by Eliot Ness, who, from 1929 to 1931, worked to end Al Capone's illegal activities by aggressively enforcing Prohibition laws against Capone and his organization. In their conduct, they became legendary for being fearless and incorruptible.

President Herbert Hoover, charged his Secretary of the Treasury, Andrew Mellon, with bringing down Al Capone. The federal government approached the problem by attacking Capone's organization on two fronts. The first front was mounted by criminal investigators of the Treasury's Bureau of Internal Revenue, who would examine the financial records of Capone and his subordinates to see if they could be prosecuted for tax evasion.

The second front would consist of a special unit of the Bureau of Prohibition, a branch of the United States Department of the Treasury and later the Department of Justice, who would attack Capone's beer and liquor empire by raiding speakeasies, stills, and, particularly, breweries.

Eliot Ness was chosen to head this elite squad.

An attempt by Capone to bribe Ness's agents was seized on by Ness for publicity, leading to the media nickname "The Untouchables".

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