Polar bear

Polar bears were a type of bear typified by their all-white pelts, and their proclivity for living in cold climates. During a mission for Santa Claus in snowy conditions, the First Doctor encountered and was menaced by a polar bear. He was rescued by John and Gillian, who used the Doctor's "magic box" to miniaturise the bear. (COMIC: A Christmas Story)

The Seventh Doctor encountered a polar bear while hosting The Ultimate Challenge. (TV: Search Out Space)

As the Eleventh Doctor attempted to use the Visual Recognition System to determine the species of a drawing of a Krafayis, it offered a polar bear as one of the incorrect identifications. (TV: Vincent and the Doctor)

The Soviet submarine, the Firebird, kept a cattle prod on board for when they encountered polar bears. (TV: Cold War)

Past
In the 20th century, polar bears were the largest land carnivore on Earth. They hunted by smell, and could travel at speeds of up to 25 miles per hour. They also had excellent smell. (AUDIO: The Wreck of the Titan)

Alternative timelines
In an alternate timeline, a mounted polar bear was one of the exhibits in the National Museum. (TV: The Big Bang)