Definition of sovereign
1 a : one possessing or held to possess supreme political power or sovereignty
b : one that exercises supreme authority within a limited sphere
c : an acknowledged leader :
https://www.merriam-webster.com/dictionary/sovereign
Definition of citizen
1 : an inhabitant of a city or town; especially : one entitled to the rights and privileges of a freeman
2 a : a member of a state
b : a native or naturalized person who owes allegiance to a government and is entitled to protection from it She was an American citizen but lived most of her life abroad.
3 : a civilian as distinguished from a specialized servant of the state Soldiers were sent to protect the citizens.
https://www.merriam-webster.com/dictionary/citizen
The "sovereign citizen" movement is a loosely organized collection of groups and individuals who have adopted a right-wing anarchist ideology originating in the theories of a group called the Posse Comitatus in the 1970s. Its adherents believe that virtually all existing government in the United States is illegitimate and they seek to "restore" an idealized, minimalist government that never actually existed. To this end, sovereign citizens wage war against the government and other forms of authority using "paper terrorism" harassment and intimidation tactics, and occasionally resorting to violence.
https://www.adl.org/education/resources/backgrounders/sovereign-citizen-movement
On February 6, the Federal Bureau of Investigation held a news conference about a growing problem faced by local law enforcement agencies. According to the FBI, police all around the country have been contacting the Bureau with requests for information and training on the sovereign citizen movement.
https://www.forbes.com/sites/jjmacnab/2012/02/13/what-is-a-sovereign-citizen/#625dfd656012
The sovereign citizen movement is considered the top threat for domestic terrorism, according to a survey of state, local, and tribal law enforcement agencies.
https://www.rt.com/usa/177892-sovereign-citizen-terrorist-threat/
The strange subculture of the sovereign citizens movement, whose adherents hold truly bizarre, complex antigovernment beliefs, has been growing at a fast pace since the late 2000s. Sovereigns believe that they get to decide which laws to obey and which to ignore, and they don't think they should have to pay taxes.
The Sovereign Belief System
The contemporary sovereign belief system is based on a decades-old conspiracy theory. At some point in history, sovereigns believe, the American government set up by the founding fathers — with a legal system the sovereigns refer to as "common law" — was secretly replaced by a new government system based on admiralty law, the law of the sea and international commerce. Under common law, or so they believe, the sovereigns would be free men. Under admiralty law, they are slaves, and secret government forces have a vested interest in keeping them that way.
https://www.splcenter.org/fighting-hate/extremist-files/ideology/sovereign-citizens-movement
Today, we look at a third threat—the “sovereign citizen” extremist movement. Sovereign citizens are anti-government extremists who believe that even though they physically reside in this country, they are separate or “sovereign” from the United States. As a result, they believe they don’t have to answer to any government authority, including courts, taxing entities, motor vehicle departments, or law enforcement.
This causes all kinds of problems—and crimes. For example, many sovereign citizens don’t pay their taxes. They hold illegal courts that issue warrants for judges and police officers. They clog up the court system with frivolous lawsuits and liens against public officials to harass them. And they use fake money orders, personal checks, and the like at government agencies, banks, and businesses.
That’s just the beginning. Not every action taken in the name of the sovereign citizen ideology is a crime, but the list of illegal actions committed by these groups, cells, and individuals is extensive (and puts them squarely on our radar). In addition to the above, sovereign citizens:
Commit murder and physical assault;
Threaten judges, law enforcement professionals, and government personnel;
Impersonate police officers and diplomats;
Use fake currency, passports, license plates, and driver’s licenses; and
Engineer various white-collar scams, including mortgage fraud and so-called “redemption” schemes.
Sovereign citizens are often confused with extremists from the militia movement. But while sovereign citizens sometimes use or buy illegal weapons, guns are secondary to their anti-government, anti-tax beliefs. On the other hand, guns and paramilitary training are paramount to militia groups.
https://archives.fbi.gov/archives/news/stories/2010/april/sovereigncitizens_041310/domestic-terrorism-the-sovereign-citizen-movement