For roughly the first 50 years after its discovery Ceres was frequently referred to as a planet: By the end of 1851 14 other similar objects had been discovered and it did not take long before these instead became known as “minor planets”. Ceres was eventually reclassified as a Dwarf Planet alongside Pluto in 2006.v

Image source: http://photojournal.jpl.nasa.gov/catalog/PIA19171