The man's given name was Temujin. "Chengis Khan" was a title and not a name and was pronounced as one word, "Chengiskhan" where the 'kh' is pronounced like a German 'ch' or Russian 'x'; Russians write the name/title "Ченгисхан". There is an interesting video in 6 parts on youtube, actually a Mongolian film dubbed into Russian, about the Mongol invasion of the Eastern Turkish (Khwarism) empire:
https://www.youtube.com/watch?v=BY_YM4JESyk&t=5s
Khwarism was one of the three or four big empires in the world at the time and the Mongols totally tore the place apart. By the time the muslim military in the region got as far as trying to organize any sort of a defense, their entire world lay in ruins around their ears.