The name Cem is not a rare name in Turkey and it comes from an ancient Persian king "Djamshid" which became as "Djam" in Medieval Persian language. It was Yima in Avesta language which means that "shining light", by the time, Y turns into J in Persian. In current Turkish alphabet, C has the sound of J or Dj.
Comes from an ancient Persian king called Jamshid which started to be pronounced as Jam during the Medieval age in Persia. In Avesta, Jam used to be Yima (lately Y turns into J) which used to mean "he who shines out". [noted -ed]
In current Turkish alphabet, C has the sound of J or Dj.