Johann Galle is famous for being the first person to spot Neptune. The planet had been calculated by Urbain Le Verrier and John Couch Adams. Le Verrier was a French Mathematician who was interested in celestial mathematics. Adams was a British Astronomer.
Urbain responding to the thesis that he had been sent, told Johann where to look for the planet and in doing so, he found Neptune. Other people had probably seen Neptune but had not known of the significance of their find. Neptunes existance had been calculated because Uranus`s orbit was wobbling by the gravitational pull of another object. He had been working as an astronomer at the Berlin Observatory when he made the discovery. Apart from discovering Neptune, he also discovered a number of comets during his time at the Observatory. Neptune`s blueness meant that being named after the Roman God of the Seas was the only logical name to confirm to the other names.