Baljinnyam's collection includes 12,000 copies of books in 58 languages. [Photo provided to China Daily]

He and his wife, Zhang Jixia, an ethnic Han, have traveled to more than 40 countries, starting from Japan, where their eldest daughter used to live.

They often gave popular tourist destinations a miss, instead focusing on local bookstores, libraries and flea markets for references about Genghis Khan.

"You cannot imagine how excited we were when we found a Bengali version of Genghis Khan's biography at an old book market in Bangladesh after days of looking around in vain," he recalls of their trip to Dhaka in 2012.

They were also surprised to find four different kinds of books on Genghis Khan in a small bookstore in Cape Town, South Africa, in 2013.

But not everywhere gave Baljinnyam what he was looking for.

He searched for such books in Cuba during one of his trips, but returned to China empty-handed. He later found out that Cuba, too, had books on Genghis Khan.

A son-in-law of Baljinnyam from Pakistan helped him get more than 100 such books from the Arab world.