Thus far i have only accumulated a short list of relatively modern books written about Khan. Does anyone know quality quotes or translations from the book, 'The Secret History of the Mongols' that provides knowledge about his reign and the way that he went about things? I am also searching for sources that show how he was able to maintain and expand his power throughout his reign. Hence far i have a list of maps depicting his movement throughout Mongolia and the ways in which he expanded.
Any help is appreciated!
Pedantry, but note that Khan is a title, not a surname, so "written about Khan" doesn't make much sense.
I've browsed though Urgunge Onon's translation of the SHOTM into English, and it seemed decent enough, but keep in mind that it was written during that era as a chronicle, so there are no philosophical discussions there (that I can recall).
European travel literature was popular during the 13th century as contact between Europe and the East became more common. Many wrote about contact with the Mongols and the Mongol court. Here are some who might be helpful for you:
Ystoria Mongalorum by Giovanni da Pian del Carpine (Probably the most helpful for you)
Itinerarium fratris Willielmi de Rubruquis de ordine fratrum Minorum, Galli, Anno gratia 1253 ad partes Orientales by William of Rubruck
Il Milione by Marco Polo
The Travels of Sir John Mandeville by John Mandeville (This work is probably derivative of others works though)
There are other works as well similar to the one by del Carpine because he was only of of many Papal legates sent to the Mongol court, but he is probably the best known.
Also, the Mongol Empire was medieval, not ancient.
The closest for philosophers writing about Genghis Khan himself would probably be the Daoist monk Qiu Chuji, who was invited by Genghis Khan, met him somewhere during his western expedition, and gave him some advice and stuff.
A couple of records by his students who traveled with him survive.
Unfortunately I don't know what they say, only they exist.
The book you mentioned is probably one of the best sources of information about Genghis Khan. It is probably one of the most reliable sources and sheds the most light on the topic of Genghis Khan. Another suggestion for good reads in the Khan series by Conn Iggulden. The series is nonfiction, yet he did a ton of research himself and gives historical notes at the end of his books to say what is known and true, and stuff he embellishes a bit. The reason I'd suggest this is because it gives detail on his ruling style and how he was able to build and maintain an empire. Other than that series though, The Secret History of the Mongols is another great source of literature and knowledge that will help answer your questions.