Kiri-kin-tha was a Vulcan scholar and follower of Surak's teachings. Kiri-kin-tha's First Law of Metaphysics is "Nothing unreal exists." (Star Trek IV: The Voyage Home; ENT: "The Forge")
This character was only mentioned in dialogue.
The "First Law" appears in the introduction to A Course in Miracles and serves as the foundation for the philosophy laid down in that text. 
According to Kirk Thatcher
, associate producer of Star Trek IV: The Voyage Home, Kiri-kin-tha was named after himself.