Clive Cussler, the best-selling adventure author and prolific explorer, has died at the age of 88. Cussler’s wife, Janet, confirmed the news on social media on Tuesday morning. No cause of death was stated. “It has been a privilege to share in his life,†she wrote. “I want to thank you his fans and friends for all the support. He was the kindest most gentle man I ever met. I know, his adventures will continue.†Per the New York Times, Cussler’s fiction and nonfiction books have sold upward of 100 million copies around the world, and he’s perhaps best known for his Dirk Pitt Adventures series, which he’s been penning since the early ’70s. Some of his other book series, such as The NUMA Files and The Oregon Files, were being expounded upon as recently as last year. In addition to writing fictional exploits about the great outdoors, Cussler was an actual underwater adventurer: He’s estimated to have led expeditions that discovered 60 shipwreck sites. “Hell, no. I’m not quitting,†he recently joked. “They may find me behind the computer, just bones and cobwebs.â€