Bai-Ülgen or Ülgen (Old Turkic: 𐰈𐰞𐰏𐰅𐰣; Cyrillic: Үлгэн) is a Turkic creator-deity, usually distinct from Tengri but sometimes identified with him in the same manner as Helios and Apollo. His name is from Old Turkic bay, "rich", and ülgen, "magnificent". Ülgen is believed to be without either beginning or end.

In Tengrism, the birch tree, regarded as a cosmic axis between earth and sky, was regarded as sacred to him, as was the horse (horse-sacrifice was a part of his worship). Ülgen symbolizes goodness, welfare, abundance, plentiness of food, water, etc. Furthermore, he created earth, heaven and all living beings. In addition, he controls the atmospheric events and movements of stars. He creates land for people to live on, the heads of both humans and animals and the rainbow. He was regarded as the patron god of shamans and the source of their knowledge.

It is believed that Ülgen has been created from Kayra (Tengere Kayra Khan). He is the highest deity after Tengri in the pantheon. Often, Ülgen is compared with Tengri and at times they are thought to be on par, or even the same. In some sayings, the name/function of Ülgen may be (partially) interchangeable with that of Tengri.