Spock's loyal pet sehlat on Vulcan, who died protecting the young Spock from a predator in the desert.
I-Chaya is the sehlat, a large furry Vulcan animal, kept by the Spock family when Spock was a boy. When young Spock goes into the desert to test himself, I-Chaya follows him and is mortally wounded fighting off a le-matya.
The adult Spock, who has returned through the Guardian of Forever to save his own life, brings a healer, but the healer can only prolong the animal's suffering. Young Spock chooses to let I-Chaya die peacefully, an early act of facing loss in the Vulcan way.