Hippalus (Moon)

Greek explorer (unkn-c. 120).

Hippalus is the remnant of a lunar crater on the eastern edge of Mare Humorum. To the southeast is the crater Campanus, and to the northwest is the small flooded crater Loewy. The southwest rim is missing, and the crater forms a bay along the edge of the mare. The surviving rim is worn and eroded, forming a low, circular mountain range. (wikipedia entry)

A crater is a circular depression likely created by an impact event. On the Moon they are named after deceased scientists, polar explorers, astronauts or cosmonauts.