Tethys came from a kingdom deep in the waters of the dreaming. So deep in fact, that no one knew for certain what existed far above the black waters that surrounded them. Tethys insisted there was more to the world that what could be seen, and was tried and imprisoned as a heretic for her beliefs. She was eventually set free by the caretaker of this kingdom’s equivalent of the House of Mystery.
Tethys same for her life, up and up and up through the dark waters until finally surfacing through a hole in the basement of the House of Mystery. Proud to have seen the world above, Tethys accepts her fate as a shark takes her to her death. (The Dreaming #33 )
Later on, after the death of Matthew the raven, Dream of the Endless reincarnates Tethys as his new raven companion. The first white raven since Lucien, the original raven who had his feathers stained black. (The Dreaming #43)
When Echo is possessed by the spirits of the Houses of Mystery and Secrets, she wages war upon The Dreaming and sends a nightmare to kill Tethys to prevent her from delivering a message to Dream. Though the creature succeeds in its attempt on Tethys’ life, Dream returns her to life soon after. Dream believes that Tethys represents his promise to take better care of the Dreaming, and letting her pass away so easily would be like breaking his promise. (The Dreaming #58 and #60)