http://en.wikipedia.org/wiki/Kushan_Empire
The earliest documented ruler, and the first one to proclaim himself as a Kushan ruler was Heraios. He calls himself a “Tyrant” on his coins, and also exhibits skull deformation. He may have been an ally of the Greeks, and he shared the same style of coinage. Heraios may have been the father of the first Kushan emperor Kujula Kadphises.
The Kushans adopted elements of the Hellenistic culture of Bactria. They adopted the Greek alphabet (often corrupted) to suit their own language (with the additional development of the letter Þ “sh”, as in “Kushan”) and soon began minting coinage on the Greek model. On their coins they used Greek language legends combined with Pali legends (in the Kharoshthi script), until the first few years of the reign of Kanishka. After that date, they used Kushan language legends (in an adapted Greek script), combined with legends in Greek (Greek script) and legends in Pali (Kharoshthi script).....they absorbed the strong remnants of the Greek Culture of the Hellenistic Kingdoms, becoming at least partly Hellenised.
PS: “Kushan” = “Kalash” ? (The group that retained the old Vedic polytheist religion while the rest of the tribe when Buddhist?
Unlikely. The Kushans were invaders from Central Asia, not Aryan Hindus or Vedists. Genetically they were a lot closer to the Huns or Mongols. They probably had a similar rudimentary shamanistic religion prior to adopting Buddhism. The Mongols themselves later mostly became Buddhists, except in the west where they went Muslim.
Interestingly the Kalash live right next to Nuristan. This area was known as Kafiristan till the 1890s. It was the last major area of Afghanistan inhabited by “pagans.” It’s the area where Kipling set “The Man Who Would Be King.”
During the 1890s it was subjected to good old-fashioned jihadi forced coversion and is now 100% Muslim.