Chiltara, The Vile Frost Stalker, is a randomly spawned Unique female Wintersbane Lacuni Huntress in the Caverns of Frost in Act III of Diablo III.
She is best known for dropping the Gibbering Gemstone, which is required to craft the Staff of Herding and gain access to Whimsyshire.
She only spawns in level 2 of Caverns of Frost and is not guaranteed to spawn. She also does not guarantee a drop of the Gibbering Gemstone. In combat, she has Orbiter and Frozen affixes.
Before patch 2.0.6, in addition to the gemstone, she also had a chance to drop either a Frozen Blood or Urn of Quickening.