Ikkaba
The Ikkaban were a highly advanced species which died out en masse.
The Ikkaban had advanced technology rivaling those of species like the People. They had even developed some simple time travel technology. Unlike other such species, they did not form empires with this technology and left behind little but poems.
The Ikkabans had a strong belief in self-immolation and built pyramids dedicated to this purpose. This was believed to be linked to a belief of reincarnation.
The Ikkabans traveled across the Mutter's Spiral, and at least three other galaxies, including the galaxy of the People. They traveled from at least 1450 BCE to at least 450 CE. During their long period of space travel, they influenced the creation of pyramids in many cultures, including the Aztecs, the Babylonians and the Yamayans. They later stopped their practice of meddling with other species and eventually, the entire civilization committed mass suicide.
After the Ikkaban died out, very little information was left about them. Many of their poems survived, though there was disagreement about the exact translations of the texts. Bernice Summerfield wrote a book called An Eye for Wisdom: Repetitive Poems of the Early Ikkaban Period in 2595 about these poems. The Ke Chedani also discovered several artifacts from Ikkaban society. (BNA: Walking to Babylon)