Strong, ferocious and scary-looking, they were on top of the dinosaur food chain.
And there could be another reason why the T-Rex is so popular: there were a lot of them, apparently.
They were everywhere!
A recent study revealed that an approximate 2.5 billion T-Rexes once inhabited earth over the course of a few million years, Livescience reported.
The research, conducted by the University of California, took into the account the size of an adult T-Rex, its sexual maturity age and also the amount of energy it needs to survive.
Based on the numbers, the team calculated that there were 127,000 generations of the T-Rex, they mature sexually at the age of 14 to 17 years, and they have a maximum life span of 28 years.
Despite the huge number (it's akin to the population of China and India combined), they did not stalk Earth at the same time.
The researchers concluded that at any one time, only about 20,000 adult T-Rexes were alive between about 68 million and 65.5 million years ago.
That's because according to the study, an adult T-Rex required a substantial amount of energy to survive due to its size, and that ultimately meant a lower population density, "around one T-Rex per 100 square km", researchers said.
Overall, the researchers roughly estimated that the population of the T-Rex could be as little as 140 million, or as many as 42 billion, with 2.4 billion as the middle value.
Why so little fossils?
At the moment, fewer than 100 T-Rex individuals have been unearthed, and only 32 of them with enough material to figure they are adults, according to Livescience.
The director of the University of California Museum of Paleontology, Charles Marshall, told the website that the population density theory was the reason behind the low number of discovery of its fossils.
If the number was just 2.5 million instead of 2.5 billion, Marshall said we wouldn't even know that the mighty T-Rex existed.
Well, thank god for the T-Rex then. Can you imagine a Brachiosaurus becoming the star of 'Jurassic Park'?