An initially terrifying creature in the Moomin series of books by Tove Jansson, the Groke is a large, slow moving, shuffling monster who is attracted to light.

She freezes the ground wherever she walks and sits, killing any vegetation.

As we get to know the Groke better, we begin to feel less scared, and more pitiful, since she is only seeking light and warmth due to her extreme loneliness.

In the original Swedish (Jansson was a Finland Swede), her name is Mårran, and in Finnish, she has the beautifully apt sounding Mörkö.

We first meet her in Finn Family Moomontroll, and she also features in Moominpappa's Memoirs (formerly known as The Exploits of Moominpappa), Moominland Midwinter and Moominpappa at Sea.

As with many Moomin monsters, we know nothing of her lineage or whether there are more than one of her.


Sources:
http://www.geocities.com/lindashippert/moomin/moominnf.html
Thanks to heyoka for additional info.