I was trying to find something nice, short and downloadable... but OK, from the horse's mouth then (so to speak):
1.Taxable Person
Taxpayers are classified into “resident” and “non-resident”. “Resident” means any person residing in Thailand for a period or periods aggregating more than 180 days in any tax (calendar) year. A resident of Thailand is liable to pay tax on income from sources in Thailand as well as on the portion of income from foreign sources that is brought into Thailand. A non-resident is, however, subject to tax only on income from sources in Thailand.
Source: https://www.rd.go.th/english/6045.html
So what is a tourist that's staying over 180 days in a calendar year in Thailand not? A "person"? Identifies as what then?
As for tax number. How do you pay tax in Thailand if you don't have Thai tax number?