Apollo or Hermes ?

Since Mercury was visible from the Earth, we wouldn't know who discovered the planet.
 There are people, of course, who made serious probes and discoveries regarding the planet. The Greeks, seeing the planet during the morning and evening
sky, had a name for it. It was called Apollo during the morning and Hermes at night. However, they did not know the two stars were actually just one object. It was later during the 4th century that the Greeks discovered that they were the same.