There are seventy-nine different species of monitor lizard on the planet, ranging in size from just about 8 inches, to over 10 feet in length. The largest and most famous monitor is the Komodo dragon. In the areas of Thailand that I visited, water monitors were fairly common. Tree monitors, however, were not and I was lucky to get a great look at this guy in the Khlong Seang Wildlife Sanctuary. He was big — not quite Komodo big — but maybe five feet from head to tail.
Nikon D500 with Nikkor 200-400mm lens (at 400mm) ISO 800, f/4 at 1/800th of a second