The roots of the "Enrolled Agent" (EA) can be
traced back to the Enabling Act of 1884. EA's are
tax professionals licensed by the Department of Treasury
and under Treasury Circular 230 are able to represent
taxpayers before all levels of the IRS. EA's are
the only tax professionals licensed by the federal
government. Their federal designation gives them access
and insight with federal and state agencies no matter where
the EA practices and no matter where the taxpayer lives.
To become an EA an individual must demonstrate special competence in federal tax matters by written examination administered by the IRS or have a minimum of 5 years of continuous employment with the IRS regularly applying and interpreting the provisions of federal tax law.
No other tax professional is required to demonstrate such comprehensive knowledge of federal tax law. Because of the difficulty of earning enrollment and the strict professional education required to maintain enrolled status, it's estimated that there are fewer than 45,000 EA's in the world.
See more at IRS Enrolled Agent Information