LONDON — Where most people saw a crumbling, rust-stained hunk of concrete and steel, Paddy Roy Bates saw a kingdom.
Mr. Bates, who has died at age 91, occupied an abandoned wartime fort in the North Sea and declared it the sovereign Principality of Sealand, with its own passports, flag, anthem, and stamps — and himself as its monarch.
What began as a swinging 60s attempt to set up a radio station became a micro-state that is still going strong more than 45 years later — although it has not been recognized by any government.
‘‘I might die young or I might die old, but I will never die of boredom,’’ Mr. Bates said in a 1980s interview.
His son, Michael, said Mr. Bates died Tuesday at a care home in Leigh-on-Sea in eastern England. He had been suffering from Alzheimer’s.
In the 1960s, inspired by the ‘‘pirate radio’’ movement of unlicensed stations broadcasting pop music from outside Britain’s boundaries, Mr. Bates set up Radio Essex on an offshore fort.
When that was closed down, he moved in 1966 to Fort Roughs, a disused World War II artillery platform in international waters about 7 miles off England’s east coast.
Michael Bates said his father initially intended to set up another radio station, but then ‘‘had the bizarre idea of declaring independence.’’ Rejecting a British order to leave, he proclaimed the fort the Principality of Sealand, declaring himself Prince Roy and his wife, Joan, as princess.
He claimed the 5,920-square-foot fort — two concrete towers connected by an iron platform — to be the world’s smallest sovereign state, though it was not internationally recognized.
Mr. Bates was tried in 1968 after an incident in which shots were fired from the platform at a British boat.
He was acquitted, with the court ruling that Sealand fell outside the United Kingdom’s jurisdiction.
Britain later expanded its territorial waters to encompass Sealand but has largely ignored the breakaway platform.
Despite the lack of legal status, Mr. Bates gave Sealand its own constitution; red, white, and black flag; passports; stamps; coins; national anthem; and motto: ‘‘E Mare Libertas’’ — ‘‘From the Sea, Freedom.’’
Today, Sealand makes money by selling aristocratic titles and hosting Internet servers.
According to Sealand’s official website, Mr. Bates fought on the Republican side in the Spanish Civil War and worked at London’s Smithfield meat market before joining the British Army during World War II, serving as an officer in North Africa, the Middle East, and Italy.
After the war he imported meat from Ireland to the north — where rationing was still in effect — imported rubber from Malaysia and ran fishing boats off England’s east coast before founding Sealand.
In his later years Mr. Bates moved to the mainland, making his son regent and head of state of Sealand.
Michael Bates remembered his father as a ‘‘huge, huge character.’’
‘‘How many people do you know that are discussed by governments and prime ministers?’’ he said. ‘‘The history is absolutely amazing.’’
Mr. Bates leaves his wife, his son, and his daughter, Penny.