The Thought Lion is a white lion with a grey mane and seemingly magical powers who was introduced in "The True Bride," an episode of The StoryTeller. In the story, he provides aid to Anja, a young woman who is under the oppression of an evil troll. He tells Anja that he comes from her thoughts. In the end of the story, she and her husband name him "The Thought Lion" and kept a statue of him which they told their children could come alive in an instant, if they ever needed him.
Jim Henson liked the realistic lion so much that it was featured as his co-host in The Jim Henson Hour, appearing in opening and closing scenes. For the most part, the White Lion did not speak in these appearances, only roared -- although he did have two lines, one in the opening scene, and the other in the closing scene of episode 108, which featured "The True Bride."
The animatronic lion was built by Jim Henson's Creature Shop and took three performers to manipulate.