Kasi is a tribe of Pashtuns which is primarily concentrated in and around Quetta city. It is also spelled as Kansi. They belong to the Saraban division of Pashtuns. It is numerically a very small tribe, they only numbered 1064 souls in 1901 AD (“Quetta-Pishin Gazetteer, 1901, p-73). They were once very numerous and held entire Quetta and Mastung districts. A large number of them migrated to India during the times of Lodi Sultans. Shaikh Jamaluddin Kasi was a noble of Sher Shah Sur who later joined a Sufi order. Tatar Khan Kasi was a high ranking noble of Islam Shah Sur and governed Rohtas fort in Punjab. 
The Kasi tribe is divided into seven sections, namely, Achozai, Ahmad Khanzai, Akazai, Badazai, Mirzai and Samungli. 
According to Ain-i-Akbari of Abu Fazal (written around 1590 AD), Shal & Mastung was dependency of Kandahar in later half of sixteenth century. Shal had mud fort at that time and its lands were assessed at four and half tumans in money, 940 sheep and 780 kharwars in grain. The Kasi Afghans and Baluchs of Shal- Mastung had to furnish 1,000 horse and 1,000 foot.
In the reign of Shahjahan (1628-1655) Rajo and Zangi, Rind chiefs raided Shal by way of the Bolan. They were defeated by the Kasis after a severe engagement about three miles south of Quetta. Since then the small stream of Zangi Lora was given its name, as the action took place at its source when Zangi, the Rind chief, was killed. 
The leading families of Kasis are known as Arbabs. In 18th century Ahmad Shah Abdali conferred the office of Arbab upon Muhammad Thalib Kasi. Mir Mahabat Khan (ruler of Kalat) killed him when he was at village Katir. The Kasi Arbab was engaged in collecting the revenue at the time and was quite unprepared for the attack. News of the occurrence immediately was despatched to Kandahar, and Ahmed Shah Durrani summoned Mahabat Khan to Kandahar to explain how he came to slay the Shah’s representative in Shal. 
Arbab Karam Khan Kasi became deputy Prime Minister of Kalat state in early 20th century. A road in Quetta is named after him.
1- “Makhzan-i-Afghani”, Dorn’s translation, p-159
2- Quetta-Pishin Gazetteer, 1901, p-7
3- Afghans of the Frontier Passes: A Study in the Historical Geography of Sibi and Dhader in the Balochistan Province of Pakistan, Volume 1, p-228
4- “Kalat – a memoirs”, by G.P.Tate, Appendix
5- “History of the Pathans” by Haroon Rashid, Vol-2, p-593