'Phags-pa, a Tibetan Buddhist lama of the Sa-skya sect, became one of Khubilai Khan's closest advisers. The two men met around 1254, and Khubilai was very impressed with the young monk. Within a short time, Khubilai became 'Phags-pa's patron and 'Phags-pa, Khubilai's religious confidante.
'Phags-pa assumed the responsibility of instructing Khubilai and his principal wife, Chabi, in the precepts of Buddhism and he was so successful that Chabi soon became an ardent Buddhist.
Acknowledging the importance of his service, Khubilai offered 'Phags-pa the title of State Preceptor in 1260 and Imperial Preceptor in1270. Eventually the Great Khan commissioned 'Phags-pa to write a book on the basic tenets of Buddhism for his son, to develop a script that could be used for many of the languages in the Mongol domains, to engage in a debate with Daoists about the merits of the two religions, and to rule over the monasteries in Tibet and eventually to govern Tibet.
The script 'Phags-pa developed, known as the "Square Script," never achieved wide popularity, but was used on paper money, seals, passports, and porcelains.
Related Web Link:
View different examples of the Square Script itself and a sample of it used in text.
More on 'Phags-pa:
Central Tibet and the Mongols, by Luciano Petech
"Tibetans in Yuan China," by Herbert Franke