Atatürk (the founder of the Turkish Republic) made surnames mandatory as a reform to be compatible with Europe (he was very pro-Europe) and this was in 1934. Everyone got to pick their own surnames. Luckily people hesitated to pick Mohammed because the word for last name in Turkish translates to "name of lineage" and that'd be a big claim (also I've heard that it wasn't allowed not to put a target on non-muslims' backs). So now we have a significant portion of the population with the surname "Pure/Core Turk" (Öztürk) and its variations (my surname Özcan included). Atatürk (father Turk) was reserved for the president though :)