The Epic of Manas "is a traditional epic poem dating to the 18th century but claimed by Kyrgyz tradition to be much older". The footer of the Wikipedia article about the epic treats it as an example of national epic poems and adds the article to the category National symbols of Kyrgyzstan.
The epic was transmitted orally for several centuries. The Wikipedia article also contains an interesting paragraph about the connection between the epic and Kyrgyz identity (emphasis added; links to sources removed):
Changes were made in the delivery and textual representation of Manas in the 1920s and 1930s to represent the creation of the Kyrgyz nationality, particularly the replacement of the tribal background of Manas. In the 19th century versions, Manas is the leader of the Nogay people, while in versions dating after 1920, Manas is a Kyrgyz and a leader of the Kyrgyz.
"Changes were made" is a group of weasel words; it is not clear who made those changes. For comparison, in Estonia, the Learned Estonian Society had the creation of a national epic as one of its goals. In Finland, Elias Lönnrot, who compiled the Kalevala, was a member of the Finnish Literature Society and the Kalevala was one of its first publications. This brings us to the question who made those changes to the Epic of Manas. Was this a society similar to those in Finland and Estonia? Who was behind the creation of a Kyrgyz identity in a time when Stalinism was very suspicious of many ethnic minorities and organised ethnic deportatations on a massive scale? (Muslim peoples of Central Asia had revolted at least twice in the first three decades of the twentieth century; see the Central Asian revolt of 1916 and Basmachi movement, so I think the Soviet authorities had good reasons to keep an eye on nationalistic tendencies.)
 Both the Nogais and the Kyrgyz people are Turkic ethnic groups; both the Nogai language and the Kyrgyz language belong to the Kipchak sub-branch of the Turkic language family. (The Tatar language belongs to the same sub-branch.)