The Cold (Time and Relative)

The Cold was an entity that existed on Earth at least as far back as the First Great Ice Age.

The First Doctor encountered it in London while he was living at 76 Totter's Lane with Susan. He was unsure whether it was a formless intelligence that could manipulate frozen water, or existed within ice itself. The Cold had lain dormant for millennia, and revived around 1963. It planned to rid the world of what it considered a mammalian infestation. The Doctor, still bound by the Time Lord non-interference policy, was going to allow it to do so. However, Susan convinced him to stop it. The Doctor used the TARDIS to reach into other dimensions and condense the Cold into a single snowflake. After several failed attempts, he managed to reach the far future and leave it on Pluto. (PROSE: Time and Relative)

Behind the scenes
Kim Newman reused the Cold in his short story Cold Snap, where it reawakened in the early 1970s. However, that story implies that the Cold exists across several dimensions. Rather than confirming that the related Anno Dracula and Diogenes Club series are set in the Doctor Who universe, the Cold Snap "crossover" simply establishes that Newman believes Doctor Who has a place in his greater fictional multiverse.