Leonardo Augustus Patterson was born on April 15, 1942, in Limon, a town on the Caribbean coast of Costa Rica. Little is known about his family history. He said that his father left home when he was very young and that his mother, a farmer, died when he was a teenager.

He said he found his first antiquity, a shard of ancient pottery, in a yam field when he was 7.

He moved to San Jose, the capital of Costa Rica, when he was 15. There, he found work with a jeweler, who tasked him with melting down gold rings and necklaces that looters brought in from unprotected archaeological sites.

But Mr. Patterson saw further potential.

“I wondered why I should be melting these old things down to make a terrible ring out of them,” he told the German magazine Der Spiegel in 2016.

After selling items locally for several years, he moved to Miami, where he imported them for local galleries. A chance encounter with a wealthy collector led to opportunities in New York, where he had moved by the late 1970s.

Mr. Patterson kept his family life largely secret. He claimed to have at least 13 children by five different women. A list of survivors was not immediately available.

Though few people doubted that Mr. Patterson had committed a long list of crimes, even some of his antagonists admitted that he had an endearing side. They cited his serene personality and his dry wit — a quiet charisma that seemed to undergird his entire career.

“He was a lovable guy,” Mr. Brand said.

When he told Mr. Patterson that he was planning to write a book about him, Mr. Brand recalled, Mr. Patterson replied, “Please, just wait until I’m dead.”

Tom Mashberg contributed reporting.