The Tuatha de Danaan are rumored to have given Humanity the ability to dream. Humanity, in turn, gave the Tuatha the raw material needed to shape the Age of Legends. From the Tuatha, all other kiths sprang forth and populated the Dreaming. But in time, as Spring gave way to Summer, the Tuatha de Dannan became bitter and secluded, approximately around the time the first prodigals appeared.
The earliest appearances of the Tuatha de Danaan in the mortal world date to the beginning of the Bronze Age in 2050 BC, forming from the dreams of a mortal people known as the Beakers that had reached Ireland. The Tuatha fought against the Adhene known as the Fir-Bholg that had populated the island, as well as their Fomorian overlords. The Tesserakonta (the War of Trees) saw the victory of the Tuatha host under Lugh over the Fomorian King Balor. The remaining Fomorians were banished beyond the Silver Path. In the time period that followed, mortal and fae lived side by side under the rule of the Tuatha who were revered and remembered as the Celtic gods of Hibernia. Numerous new kiths came into existence during this period and the Tuatha were rumored to travel the world to grace other human cultures with their inspiration.
Critics among the Tuatha pointed out that their close proximity to the humans made them weak and left the humans jealous and greedy for the power and beauty of their overlords. To assuage these fears, the Tuatha took it unto themselves to visit the world of flesh only seasonally, otherwise spending time in Arcadia within the Deep Dreaming. In their absence, leadership fell to their chosen representatives, the Sidhe. Noble Houses dedicated and founded by one of the Tuatha congregated and rivaled with each other.
Around 500 BC, the fae had become so enamored in their own power struggles that they failed to recognize a shift among the human population. Many failed to thank the Fae for their help or even demanded it. Seelie and Unseelie argued about what to do, with the Unseelie pushing for war to put the humans back into their place. Amidst these struggles, a new Celtic tribe arrived in Ireland, the Míl Espáine, also known as the Milesians. Originating from the Iberian Peninsula, the Milesians quickly came to dominate the Celtic tribes of Ireland.
The Milesians and the Tuatha came to blows. The seasonal shift meant that the more fierce Unseelie were forced to retreat to the Dreaming and leave their more passive Seelie cousins in control. Some, feeling that the Dreaming and the mortal world had drifted too far apart, counseled a full retreat. Meeting the Milesians in honorable warfare, the Tuatha quickly learned that their bronze weapons worked little against the iron used by their enemies, as well as the deadly power of Cold Iron to themselves. Following their last battle at Tailtiu, the remaining Tuatha fled to Arcadia, leaving their children behind.
In the Time of Judgement, the Tuatha appear either as benefactors to their descendants, or as enemies, who feel that the modern Changelings are abominations and violations of an oath against the mingling of fae and human blood.
In Irish mythology, the Tuatha Dé Danann are the race of fey or divine beings that originally inhabited Ireland; the name "Tuatha Dé Danann" means "people of Danu". Changeling: The Dreaming books consistently use the (mis)spelling "Tuatha de Danaan" in reference to the Tuatha. A sidenote on "de" versus "Dé". In Irish "Dé" is not possessive, in this context it refers to a divinity, a god or goddess. Therefore something like "People of the goddess Danu".