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"
Trespasser Storyboard image of Greenwood
Hidden inside the Dam on the Trespasser version of Isla Sorna a skeleton of Harold Greenwood can be found. The deceased starved while hiding from Velociraptors, after he'd managed to crawl into the dam losing blood.
Harold Greenwood would've played a bigger part of the cut level Plains where according to a 1997 "walkthrough" is where Anne would hunt down a T-Rex to get a battery for the electronic device found at Greenwoods body. Hammond mention Harrold Greenwood in some more recorded voiceovers:
Harry claimed to be a friend of my former son-in-law. I liked him – he was confident, dashing.
Greenwood carried some sort of electronic device, which we are told he built himself, based on plans he found on the internet.
Hammond's full script reveal some unrecorded lines adding some to Harold's story:
Sources say Harry later attempted to penetrate to the interior of the island. His plan was to reactivate the geothermal plant, then to gain access to the protected data at the main lab.
A background check on Harry Greenwood revealed nothing out of the ordinary: a community college education, a gun permit.
Some effort was made to track Mr. Greenwood, but we never discovered what happened to him.
He thought he would be a hero, an explorer, a Lawrence of Arabia braving danger. He did not understand what danger really is, how easily and unexpectedly death can come.
According to an unused Anne voiceover, Harold might have been a marine:
Greenwood, Harold, USMC. Looks like it came from a novelty shop.
There have been some fan theory that Harold could've been a spy of Biosyn who came to the island with the crashed Biosyn helicopter that can be found elsewhere on the island; although there are no proof of this theory from any of the recovered design documents or game files.