What the largest predator that ever lived is depends on what you regard as a predator. There are various definitions of predation floating around, but it's safe to say that anything that consumes other animals for food is a predator. Under this broad definition, that largest predator that ever lived is the blue whale, which consumes several tons of plankton every day. This plankton includes both algae and organisms such as krill.

The blue whale weighs up to 180 tonnes and individuals up to 29.9 m (98 ft) in length have been found. It is thought to be not just the largest predator that ever lived, but the largest animal in general. However, a whale that filters krill with its baleen is not generally what people think of when they hear the word "predator."

For those unsatisfied with the blue whale, there are also at least three other very large predators that have a chance of vying for the title of largest predator if whales are excluded: an unidentified pliosaur called the Monster of Aramberri, 15 meters (49 feet) in length (contrary to earlier exaggerated estimates), Spinosaurus, the largest known predatory dinosaur, 18 m (59 ft) long, and the titanic shark Megalodon, at 18.2 meters (60 ft). The most terrifying are the last two, which had tremendous bulk and would have needed to eat many other animals to sustain it. All three are sometimes called "the largest predator ever," but as mentioned above, that title goes to the relatively unexciting blue whale.

Spinosaurus was a huge theropod dinosaur with a large tail sail and an elongated, crocodilian skull. Spinosaurus was the largest predator of the Mesozoic. It weighed 7-9 tonnes and lived during the Cretaceous period, 100 to 93 million years ago. A few skeletal fragments have been found in Egypt and Morocco. Spinosaurus primarily ate fish, though it would have consumed small herbivores and scavenged for carrion.

If I could vote for the most ferocious predator of all time, I would choose Megalodon. This was a shark so huge that the height of its tail fin approximately equals the length of the Great White Shark, the largest shark alive today. How such a monstrous creature could have even evolved boggles the mind. Its teeth, which still wash up on shores occasionally, are larger than a man's fist. Megalodon lived between 18 and 1.5 million years ago, quite recent in evolutionary terms, which has prompted some crytozoologists to hypothesize it might still be alive, though no evidence has been found to this effect.