Eduardo M. Rivera was a lawyer who sold "reliance letters" that people could supposedly rely on to avoid criminal penalties for failing to file returns (which Rivera claimed that they were not required to file).
Rivera appears to rely mainly on jurisdictional arguments, such as that Congress has no power to impose any tax outside of the District of Columbia and other "federal areas".
The United States also sued him in federal court over his sales of his "tax reliance" package, and he was permanently enjoined on July 21, 2003. United State v. Eduardo M. Rivera, No. 03-2520 (U.S.D.C. C.D. Cal. 7/21/2003). He didn't stop, however, and was found to be in criminal contempt on 12/20/2006 and sentenced to 60 days in prison. United States v. Eduardo Marmolejo Rivera, No. 2:06-cr-00624 (C.D. Ca. 3/26/2007), rev'd No. 07-50163 (9th Cir. 7/17/2008). Although Rivera's appeal to the 9th Circuit Court of Appeals was successful, he was ordered to begin serving his sentence while his appeal was pending and was imprisoned from 4/26/2007 to 6/22/2007.
At the trial of Richard Simkanin, Rivera testified that Simkanin had consulted him in 1999, and that Rivera advised Simkanin that he was not legally required to withhold taxes from his employees, advice for which Rivera was paid $10,000. Despite (or perhaps because of) Rivera's advice and testimony, Simkanin was convicted of willfully failing to withhold taxes from his employees.