Tyrannosaurus rex lived in what's now western North America roughly 68 to 66 million years ago, right at the very end of the Cretaceous Period — meaning it was one of the last dinosaurs on Earth before the asteroid impact wiped out all non-avian dinosaurs.
Built for power, not speed
Adults reached roughly 12 to 13 meters (39–43 ft) long and stood about 4 meters (13 ft) tall at the hips. Its skull alone could be over a meter and a half long, packed with thick, banana-sized teeth built to crush through bone rather than just slice flesh. Its bite force is estimated among the strongest of any land animal ever measured, living or extinct — some studies put peak bite force at over 6 tonnes.
Its arms, by contrast, were famously tiny — each barely longer than a human arm, with only two clawed fingers. Scientists still debate exactly what they were used for, though grappling with prey at close range is one leading idea.
Not just a scavenger
For a while, some researchers argued T. rex was mainly a scavenger rather than an active hunter. Most paleontologists today think it was both — a powerful enough predator to take down large prey, but also opportunistic enough to steal a meal when one was available, much like many living predators.
Why it matters
T. rex is by far the best-studied dinosaur, with dozens of reasonably complete skeletons found — including "Sue," one of the most complete T. rex skeletons ever discovered, now on display at the Field Museum in Chicago. That wealth of fossils is a big part of why it's the dinosaur most people can picture instantly.