XI'AN -- A new set of books, considered the most complete versions of the Tibetan epic King Gesar, was released Saturday at a book expo in Xi'an, northwest China's Shaanxi Province.

King Gesar is generally considered the world's longest folk epic. The collection, with over 130 million characters and 300 volumes in hardback covers, almost includes all the versions of the epic that are available, according to its investor Sichuan Publishing Group.

"It took ten years to collect all these books, including many historic versions of the epic, and many of which are debuted for the first time," said Luo Yong, chairman of the Sichuan Publishing Group.

These books have also added illustrations of Thangka and artifacts from the local museum, according to Luo.

The Epic of King Gesar tells the story of how an 11th century Tibetan demigod king conquered his enemies and helped ordinary people.

The epic has been passed down orally by singers and illiterate herders or farmers from southwest China's Tibet Autonomous Region, north China's Inner Mongolia Autonomous Region and the northwestern province of Qinghai. It was listed as a UNESCO World Heritage in 2009.