The largest animal that has ever existed is the blue whale (Balaenoptera musculus). Blue whales can reach lengths of up to 100 feet (30 meters) and weigh as much as 200 tons, making them the largest known animals to have ever lived on Earth. These marine mammals inhabit oceans worldwide, spending most of their lives in deep waters. They primarily feed on tiny shrimp-like animals called krill, consuming up to 4 tons of them daily during feeding seasons. Despite their massive size, blue whales are known for their gentle nature. However, they are considered endangered due to past whaling practices and current threats like climate change and ship strikes.