Imagine if the mysterious patron in the tavern was a Lich, High Priest of Evil or Dragon (suitably disguised, with alignment masking gear). The early missions are getting rid of rivals and/or unrelated evils that are attracting attention from afar.
The High Priest is LE, and is concerned that the CE cult is pulling away some NE worshippers or attracting attention from Paladins.
The Lich is looking to re-assemble a famous holy artifact, so it can desecrate it and use it in an unholy ritual. The artifact was broken into pieces, which somewhat less competent evil forces have taken into their possession. Perhaps the final piece is in the hands of a secret good or neutral organization - one the PCs won't recognize as an ally. (Think of the guys guarding the Mummy's crypt in the movie, they weren't exactly "good" in their treatment of people who wandered into the area, but they were better than the Mummy).
The Dragon wants money and territory. Injured/cursed in a prior combat with a rival, it is now weaker than the other, more powerful dragons in the area. It's hoping that the PCs can eliminate its rivals, and give it a cut of their treasure, with it acting as patron. It provides them a map to the locations of a dozen secret dragon hordes. When they kill the powerful dragon that had cursed it, their "patron" can reveal himself - now more powerful than ever - and perhaps burn down the town around them in thanks.
