The Blue Whale, Balaenoptera musculus, is the largest mammal living today.
It is also the largest mammal to have ever lived.
In fact the Blue whale is the largest animal ever to have lived on the planet as far as we know; bigger by far than ever the largest Dinosaur. The longest Blue Whale ever measured was a female, 33.58 m or 110ft long. The heaviest weighed over 190 tones.
We haven't actually got a set of weighing scales big enough so weights are estimated from the cut up remains.
The largest animal on land at the moment on this planet is a mammal; the bull African Elephant.
The largest specimen recorded stood around 3.96 m or 13ft at the shoulder and weighed over 12 tones.