The Sthavira nikāya (Sanskrit: स्थविर; traditional Chinese: 上座部; ; pinyin: Shàngzuò Bù) literally "Sect of the Elders," was one of the early Buddhist schools. It was one of the two main movements in early Buddhism that arose from the Great Schism in pre-sectarian Buddhism, the other being that of the Mahāsāṃghika school. The Sthavira sect was also called Sthāvirīya.
Most sources place the origin of the Sthaviras to the Second Buddhist council. Traditions regarding the Second Council are confusing and ambiguous, but it is agreed that the overall result was the first schism in the Saṃgha, between the Sthaviras and the Mahāsāṃghikas, although it is not agreed upon by all what the cause of this split was.
One suggested cause of the Great Schism were the disagreements in the five theories about an Arhat supposedly put forward by Mahādeva, who later founded the Mahāsāṃghika. The monks who rejected the five theories named themselves as "Sthavira" to differentiate from the Mahāsāṃghika. However, this account relies on a later text, the Mahāvaṃsa. Vasumitra's Samayabhedoparacanacakra, an earlier source whose writing probably dates from around 100 CE, and which is preserved in Chinese and Tibetan, there is no mention of any such person named Mahādeva. Instead, it lists the names of the well-known figures who accepted or rejected the five theories. Étienne Lamotte has also demonstrated that the existence of the "Mahādeva" character was a later sectarian interpolation.(p. 42)