Born in Semarang, Central Java, Dutch East Indies (now Indonesia), he became the wealthiest person in Asia at the start of the twentieth century.

He served as Luitenant der Chinezen in the Dutch colonial administration in Semarang, and was raised to the rank of titular Majoor upon retirement.

His father, Oei Tjie Sien, was a Chinese-born, or totok, migrant and a self-made, 'new money' businessman with no kinship ties to the colonial Chinese establishment (the 'Cabang Atas').

It has been estimated that between 1890 and 1904, Kian Gwan made a profit of some 18 million guilders in the opium trade alone, which provided the basis for his empire.

Oei's initial strategy was gradually to build up dominance in the highly lucrative opium market towards the end of the nineteenth century.

[7][8] This feat was all the more remarkable given the virtual control of the opium monopoly by more established, older concerns with close ties to the Cabang Atas.

[7][8] This auction has gone down as one of the most competitive in history, described by the poet Boen Sing Hoo in his Boekoe Sair Binatang ("On Animals", published in 1895) as a real "peperangan diantara raja-raja" ("battle of kings").

In 1912, Kian Gwan, the trading branch of the conglomerate was capitalised at fifteen million guilders, double the amount of the largest Dutch firm Internatio.

Due to the cautious and independent strategy, the company survived the subsequent sugar crisis while many other Chinese firms perished.

Besides making use of written agreements and a modern accounting system, Oei also diverted from yet another Chinese business practice of the time.

[5][9] In 1920, Oei left Semarang and settled in Singapore to escape Dutch colonial succession law and tax regime.

In 1964, the government formed a holding company named PT Rajawali Nusantara Indonesia to run them, which is still a prominent corporation up to this day.

Wellington Koo), Goei Bing Nio (Chinese: 魏明娘; pinyin: Wèi Míngniáng) was selected by Oei Tiong Ham's mother to be his wife and was married to him at the age of 15.

The younger of the two sisters, Lucy Ho (or Hoo Kiem Hoa), moved to Singapore with Oei Tiong Ham and lived with him until his death.