The largest animals that ever lived on earth would be Dinosaurs which are now extinct.
The largest known Dinosaur to ever live on earth was the Patagotitan Dinosaur which was a genus of titanosaurian sauropod dinosaur from the Cerro Barcino Formation in Chubut Province, Patagonia, Argentina.
However the largest known living animal that is still living today is the Blue Whale.
The Blue Whale which is as of now the biggest and largest animal to live on earth is a marine mammal belonging to the suborder of baleen whales.
At 30 metres (98 ft) in length and 180 metric tons (200 short tons) or more in weight, it is the largest known animal to have ever existed.
There might be a larger animal that could have existed other than the dinosaur but as of now we have no evidence of any larger animals.