@Christopher *******
you mean Bangkok Bank. There are other banks that are as popular as BBL: Kasikorn, SCB, TMB are good examples (especially outside of the Bangkok area). UOB is also very popular as it is singaporian with branches in the region.
Not sure what an agent will do for you.
Just go to the bank with your passport.
If you donāt speak thai, choose a large branch as they probably have someone speaking english + experience in dealing with foreigners.
You might be able to open an account without a resident visa in a few branches in tourist areas and/or largest branches.