Green’s Dictionary of Slang

wallah n.

also walla, waller, whallah
[Hind. sfx wala, pertaining to or connected with, and comes in turn from the Arabic wal, proximity. It is the equivalent, therefore, of the Lat. -arius. Although found today as a single term, its 19C uses tended to be in combinations, such as Agra wallah, a native of Agra, banghy-wallah, a porter who carries loads with a banghy, or shoulder-yoke, howdah-wallah, an elephant accustomed to carry a howdah, and the Anglo-Indian competition wallah, those who entered the Civil Service competitive exams, established in 1856 to replace the old system of personal patronage]

1. [mid-18C+] a man, esp. in sense of a man who is pertaining to or connected with something, usu. a job.

2. [1910s] an Indian soldier.

3. [1970s] a thing.