Sonbai Besar or Greater Sonbai was an extensive princedom of West Timor, in present-day Indonesia, which existed from 1658 to 1906 and played an important role in the history of Timor.
The origins of the princedom are intimately connected with the struggle between the Dutch and the Portuguese for mastery of the island. The united Sonbai (Sonba'i, Sonnebay) realm, the traditionally most prestigious polity among the Atoni people of West Timor, allied with the Portuguese in 1649-1655, and then with the Dutch East India Company (Vereenigde Oost-Indische Compagnie or VOC) in 1655-1658. After a series of defeats at the hands of the Portuguese Eurasians or Topasses in 1657-1658, Sonbai broke up in two parts. One group migrated to Kupang where the Dutch had their base, where they formed the Sonbai Kecil princedom. Another group, Sonbai Besar, stayed in the inland of West Timor under Portuguese surveillance.
The Sonbai Besar congregation was headed by a ruler known to the Europeans as emperor (keizer, emperador). He was also known as Atupas (he who sleeps), Neno Anan (son of heaven) and Liurai (surpassing the earth). The other Atoni rulers related themselves to him in symbolic kinship terms, which was anchored through various origin stories. In accordance with Timorese custom, the ruler was an inactive, in a symbolical sense "female" (feto) figure. At his side was a "male" (mone) executive regent of the Kono family, called Uis Kono or Ama Kono. Because of this arrangement, the princedom was often known under the name Amakono. The Uis Kono in particular governed the north-eastern part of the realm, later known as Miomaffo. The central area, Mollo, was governed by co-regents of the Oematan family, and in Fatuleu further to the west a number of lesser lords dominated, among them Takaip. Under the major lords (usif) were the amaf naek (great fathers) who headed various districts, and under them the amaf (fathers) in the various villages.