Not everyone has one
Indonesian naming is remarkably varied, and many Indonesians have no surname at all — a single name is common, especially among the Javanese (the country’s largest group), where figures like Sukarno and Suharto went by one name.
Clans, Sanskrit and Arabic
Where family names exist, they come from several traditions: the Batak of Sumatra carry inherited marga (clan names) like Nasution, Siregar and Simanjuntak; many names derive from Sanskrit (Wijaya, “victory”; Kusuma, “flower”; Pratama, “first”); and, as the world’s largest Muslim-majority country, Indonesia also uses many Arabic names. Balinese names, meanwhile, often mark birth order (Wayan, Made, Nyoman, Ketut).