"I know it's nearly four, J'onn"

J'onn J'onzz, or the Martian Manhunter, is one of DC's oldest continuously-active superheroes, a founding member of the Justice League, and a member of almost every incarnation since. While it had already been implied in Dream's encounter with Nada that he is perceived differently by each culture, J'onn's recognition of him is the first and best evidence that Dream has been known in all cultures and all times.