The Yuli were members of the Sentient Milieu (23,000 to 20,000 BCE). No fragments from the Milieu era detailing any information about them other than their name has yet been found.
Comments made by the Slylandro may indicate that the Yuli, along with the Ur-Quan and the Drall, made regular visits to thier homeworld known as Source while the Sentient Milieu was still intact. Acording the the Slylandro the varius races of the Sentient Milieu visited the Planet source for about half a Drawn which is roughly 2,500 years. This indicates that the Yuli and the rest of the Sentient Milieu were in contact with the Slylandro for most of the time that there alliance was functional. Unfortunatly the Slylandro only mentioned that the Yuli visted them and give no other details about them.
The only other information available about the Yuli comes from the present Ur-Quan races during the Dnyarri Slave Empire (20,000 to 17,000 BCE) is that the capricious Dnyarri slave masters, deciding that they and the Drall were inferior species and unworthy slaves, had them destroyed by the Ur-Quan and the Mael-Num. After this the Xen-Weyi became slave shielded at some point. Also like the Slylandro, the Ur-Quan dont give any information about them either only saying that there ansestors killed them off due to the Dnyarri's mind control over them an that later on they went on to kill or en-slave other sentient races.