Who Discovered Neptune - Solving the Mystery?

Gazing at the starry skies will never reveal one of the planets in our Solar System. If this is so, how were scientists able to localize it long before the telescope was invented?  More so, who really discovered Neptune?

According to NASA, Neptune is the eighth planet orbiting the sun and owner of the largest orbit of 165 Earth years. The gas giant is too dim to be seen with the naked eye despite its colossal size of nearly four times the size of our home. This also makes it the fourth-largest planet discovered to date.