The prince spent the last years of his life in Spain with his wife of half a century, The Daily Telegraph reported. Their son, Michael, has been serving as Sealand's prince regent, although he spends little time in his North Sea domain, preferring to hire a caretaker.
Bates had a life full of adventure, including fighting in the International Brigades in Spain in the 1930s and serving as a British army officer in World War II.
After the war, he was involved in a number of business enterprises, including importing meat and rubber, owning fishing boats and running a chain of butcher shops. In 1966, he tried to start a 24-hour pirate radio station on another military platform.
Bates created Sealand 7 miles off Felixstowe on the east coast of England after a 1967 law barred British citizens from working for pirate stations.
Sealand has had a peaceful history for the most part. Bates was charged with violating firearms laws by firing a warning shot at a government ship, but a judge ruled in 1968 that Seaman was outside British jurisdiction.
The West German embassy sent a diplomat a few years later to get one of its citizens released from Sealand. Bates, holding the man after a business dispute, granted him a royal pardon.
In later years, Bates sold Sealand passports -- he stopped because they were being used for fraud -- and offered noble titles for a few pounds.
"Listen, old boy, I like a bit of adventure. It's the old British tradition," Bates said in a 2000 interview. "Maybe Britain's changed, but there's a lot of us still about."