Enrolled Agent

An enrolled agent is a federally authorized tax practitioner empowered by the U.S. Department of the Treasury to represent taxpayers before the IRS.

 Enrolled Agents are the only federally licensed tax practitioners specializing in taxation and have unlimited rights to represent taxpayers before the IRS. Enrolled Agents must complete many hours of continuing education each year to ensure they are up-to-date on the constantly changing tax code and must abide by a code of ethics. When you need a true tax professional, see an enrolled agent.

Link:

What is an enrolled agent? (NAEA)

IRS: Understanding Tax Return Preparer Credentials