A friend of John Hammond in the game Jurassic Park: Trespasser. Harold probably went to Isla Sorna with an 'electronic device' after the Isla Nublar Incident, but before the events of The Lost World. In his memoirs, Hammond describes their first meeting:
"I first met Harold Greenwood in 1992, he was a, an American. Introduced to me as a former Green Beret. He asked a number of questions about the disposition of the InGen Technology. Harry claimed to be a friend of my former son-in-law, I liked him. He was confident, dashing. Greenwood carried some sort of an electronic device which we were told he built himself, based on plans he found on the internet"
While it's still speculation to assume the skeleton and Harold Greenwood are one-in-the-same, it's generally accepted. Harold probably was a spy of Biosyn who came to the island with the crashed Biosyn helicopter that can be found elsewhere on the island; although, according to some unused sound files he was a U.S. Marine.